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1 - University of North Carolina at Chapel Hill

1. RECOVER area POOL2 structure 1 POOL2 BASED PL2 PTR DRO OE cci de kc oko ood dc ook e OR Io oi tole lelejoeoletetelokeeloleteler POOL2 is the second half of the run time storage space for character string variables See the declaration for SCB and POOL1 for information i Figure 12 La PN XINCLUDED from DCLLIB PLZ2DEF RR EO FIO oko EEE EEEE oko totokotc EEES E OIRO EEEE EEEE S 2 POOL2DATA CHARACTER 2036 Template for a Block of String Variable Storage 39 1DCL 1 LOGRECORD BASED LOG_PTR fk hok o ee EERE ok ke ke ok ok sk sc oi ke ok ok oo de ode EERE EK EEE RE EEK EERE EK EK EEE EEE Bach student s log file is a chain of LOGRECORDs The first LOGRECORD of each chain is pointed to by MAINFILE LOGFILES Each LOGBECORD occupies one CAIFILES region 7 GZINCLUDEd from DCLLIB LOGRDEF JERR AIO RIO oboe kc jojo coke ok oko ook oc A to EE IO OR Sk ROK LOGFILE HEADER the first 16 bytes of each LOGRECORD 2 COURSE CHAR 6 Name of course this student is in 2 STU ID CHAR 9 THE FIRST BLOCK OF A GIVEN STUDENT S LOG FILLED BY LOGGER DURING AN OPEN OPERATION 2 FLAGS 8 BiT 1 INDICATOR DESCRIBING THIS SESSION FLAGS 1 0 B IF SESSION IS A RESUME x 1 B IF SESSION IS A RECOVER FLAGS 2 THRU FLAGS 8 ARE UNUSED DATA 2 ENTRIES CT FIXED BIN 15 0 Number of entries in
2. i i 11 PROC NAME i not implemented 12 PLISUB 4 not implemented 13 GLOBAL CCNAME i not implemented 14 GLOBAL INT VAB i not implemented 15 ARRAY i not implemented i i i SOROR coke e EERE joke f e oe e REE dad i e e e oe e do toe obo oce oe e toe e ec GE oe too e kE ke k eoo The following is a list of information needed to be retained from one author session to another 2 P COUNTER FIXED BIN 15 0 Next free location page offset in INSTN PART OF OBJCODE BEING BUILT 2 SYM FREE FIXED BIN 15 0 2 INT FREE FIXED BIN 15 0 a 2 STR FREE FIXED BIN 15 0 FOLLOWING IS NEEDED TO COMPILE 2 SH LAST BIT 1 Next free element in this syabol table 7 Next available element in the run time integer storage area SCB STORAGE INT E i Next free element in the list of string pointers SCB STORAGE S PTR CONTROLLING SHOW INFORMATION 2 CTRL_SW BIT 31 FOR CONTROLLING SHOW SIGNALS PROC AUTHOR T0 GO CHANGE LAST INSTRUCTION A NOP GENER ATED BY PREVIOUS DIAL STATMT TO A ZEROUNREC 2 UNREC P FIXED BIN 15 0 2 REP STACK 10 PIXED BIN 15 0 2 REPEAT STACK TOS FIXED BIN 15 0 2 SYM SPARE 23 FIXED BIN 15 0 2 FILL CHARACTER 600 Not used exists just to bring the structure up to the size of one CAIFILES region 2036 bytes Figure
3. For a description of the JCL and INCLUDES necessary to use EQDQ and ENQ DEQ facilities consult the header para graph in the EQDQ source listing For a brief explanation of the EQDQ module see its description in Section 2 16 of this manual 8 2 DATASET BACKUPS AND RESTORATIONS Regular backups should be taken of each of the files The backup and restoration procedures are well defined and well documented in the CAI Operations Manual Note that when the CAI daily jobs are running backups are automati cally made Otherwise they must be done by submitting batch jobs described in the Operations Manual Of course backups are only advisable when there is any system work test or production currently in progress a 60 Chapter 9 THE CAISYSTEM UTILITY PROGRANS In addition to the on line routines of the CAI Systen several other programs exist to maintain CAI files to pro duce reports and to serve as tools for other prograas This chapter briefly describes the function of each of these utility programs For each program a list of XINCLUDEd modules on the DCLLIB PDS will be listed followed by a list of ali the external procedures called All are described nore fully in the CAI Operations Manual the appropriate section number will be given for each program The source code for all of the utility programs resides on the PDS UNC CS E557C CAI UTILITY SOURCE 9 1 ON LLEE PRODUCTION UTILITIES These programs are
4. FIXCAIF adds blocks to the free block list This should be done by the on line systen but it isn t always A block may be no longer used but somehow not returned to the list By running MAPCAIF see below one can ascertain which blocks are no longer used yet not in the free block list Bunning FIX CAIF returns them to that list XINCLUDEd members EQDQEXT Procedures called HEADER INIT EQEXT DQEXT Reference Section 4 3 4 FREEBLK a subroutine Given a block aumber it returns that block of CAIFILES to the free block list INCLUDEd members PERHDEF Procedures called ALLOTOR Reference Section 4 3 5 HEADER a subroutine Causes the printing of a CAI header line at the top of a page of output Reference Section 7 3 1 LOCATE given a string of data fields delimited by LOCATE picks off the leftmost field This is useful because the input to other utilities such as CCBHAINT is just such a string of fields Reference Section 7 3 2 MAPCAIP prints a block accounting map of CAIFILES SINCLUDEd members MAINDEF ACBDEF CCBDEF LCBDEF LOGBDEF SCBDEF PLIDEF BTOPDEF BSECDEF Procedures called HEADER INIT EQEXT DQEXT Reference Section 4 4 2 PASSWED a subroutine Called by on line password protected programs PASSWRD asks for an author id validates it and then moves the cursor offscreen and requests a password if the password is correct for the invoking program a para
5. RESUMEDUMP file 2 C_POOLIBLK FIXED BIN 15 0 Next block in student s 43 Figure 14 RECOVDUMP file A Student Control Block 44 my DCL 1 LCB BASED LCB_PTR Soo ko oe A cete KEEK KE EEK EKER de oeeitetokeooketeoxoleeeo eee BER EERE REE EEEE EEE 7 There is a Lesson Control Block or LCB for each lesson in the CAI System whether it is attached to a course or in an author s library The LCB for each lesson points to ail the source and object code blocks for that lesson and contains the usual direc tory information like how many source code blocks there are and does this lesson need recompiling etc If the lesson is one that is attached to a course then this LCB is pointed to by that course s CCB If it is in an author library then this LCB is pointed to by the ACB INCLUDEd from DCLLIB LCBDEF n d oF ud J BEEBE ERERE ERE REE EK oot KEE EKER KEK EK HERE EKA toc EK BEEK EKE EEK KEKE KEK EK EKKER SE P8 Rol ol qe doe iore ok aie aee e ERE oie dee CR e oe poke io ee ac EK doce EHH EYE HRA REE KE EK Object Code Part ed LS BEEEEREEEEER EER ARE i aie EEK EEE EE KEKE EEK AEE eoe tok KEK RKK EEE EK ERE ERE 7 2 C SYM B BLK FIXED BIN 15 0 The CAIFILES block numbers 2 C SYM D BLKf FIXED BIN 15 0 where this lesson s cospile T time symbol table C SYM BCD and C SYM DOPE respectively are stored These block
6. Tells which section of the stack is the last one used i e shich section is the stack bottom Varies from 0 to 7 2 FREE BLOCKS 1000 FIXED BIN 15 0 Sections 0 and 1 of the stack Section 1 is defined to be FREE BLOCKS 501 thru FREE BLOCKS 1000 inclasively while Section 0 is 30 FREE BLOCKS 1 thru FREE BLOCKS 500 inclusively Section 0 fills up from from the bottom i e FREE BLOCKS 500 is filled before FREE BLOCKS 499 when PREE_BLOCKS 1 is filled Section 0 is ull and a section shift must occur 2 FILL CHARACTER 32 Not used brings the structure up to 2036 bytes the size of one CAIFILES region Figure 6 FBL TOP Region 4 of CAIFILES 31 DCL 1 FBL SECTION BASED FBL SEC PTR J BEEK kc oe ok ERK ot doc oleo o e cook eee EE ERE ERE REE ERE EEE EE REREEAEEEEK FBL SECTION is what each of the remaining sections 2 thru 7 of the FBL stack look like These sections reside on Regions 5 thru 10 of CAIFILES None of the elements of any section is ever handled individually rather an entire section may be shifted all at once SINCLUDEG from DCLLIB BSECDEF J ERERE oko se see bc ole ke ob ke t ke be ke e dele doe joo EE EES ELAS CHAERERKE EER xoc eeke tole EKER EE 2 FREE BLOCKS 500 FIXED BIN 15 0 The list of the 500 free biocks held in t
7. Each system knows which version it is by calling the external procedure SYS SW There are two versions of SYS SW one returns a true bit and is stored in the module STUONLI The other returns a false bit and is stored in the module FULLCAI Naturally the module STUONLY is linked into the student only version and FULLCAI is linked iato the full blown edition When an author signs on to the sys tem the SNONOFF module calls SYS SW If 1 B is returned a student only message is displayed and the sign on fails 2 3 1 GENERATING THE PULL SYSTEM CAIAUTH The full student author CAIAUTH system is generated as follows jobname JOB acct name paras PW spassword PA EXEC PLFPLD PARM L XREP LIST MAP RENT L SYSLIB DD DISP SHB DSN UNC CS E557C CHAT PL1LIB ji DD DISP SHR DSN UNC CS E557C CHAT SYSLIB Jf DD DISP SHR DSN SYS1 PLILIB L SYSLMOD DD DISP SHB DSN UNC CS E557C CHATJCL CAI LOADLIB YOL L OLDMOD DD DISP SHR DSN UNC CS E557C CAI SYSLIB L SYSIN DD INCLUDE OLDMOD SNONOFF INCLUDE OLDAOD AUTHOR INCLUDE OLDMOD ACBPROC INCLUDE OLDMOD SOURCE INCLUDE OGLDMNOD TABLES INCLUDE OLDMOD COMPLER INCLUDE OLDMOD CODEGEN INCLUDE OLDMOD EX ECTOR INCLUDE OLDMOD CAIMAIN INCLUDE OLDMOD CC30IO INCLUDE OLDMOD LOGGER INCLUDE OLDMOD ALLOTOR INCLUDE OLDMOD FILEIO INCLUDE OLDRKOD PATPROC INCLUDE OLDNOD EQDQ INCLUDE OLDMOD FULLCAI ENTRY IHENTRY NAME CAIAUTH R EA The order of the included o
8. The two new features are integer subtraction and the RESEQUENCE command Just as tne IF THEN and DO WHILE Stateaents appeared in the DIAL grammar but were never actu ally implemented neither was most of the arithmetic expres sion evaluation mechanism Since integer addition was already in place it was a simple matter to mirror the pro cess and implement subtraction The RESEQUENCE command allows an author to renumber the Statements in a ieas according to a given starting value and increment Implementing that command brought about an unexpected change to the system architecture elsewhere It turned out that renuabering a lesson was a decidedly asontri vial task if as was the case each statesent s number field was not of uniform length For instance 1 DCL J INTEGER and 0001 DCL J INTEGER are both equally valid representa tions of statement number one of some DIAL lesson However 21 the renunbering became quite straightforward when one assumed numeric fields of constant length Because the sys tem limits statement numbers to positive integers not exceeding 9999 I adopted the policy of four digit number fields for all statements In addition to the gain in ease of renumbering this policy has a valuable human engineering effect It aids an author in preparing more readable DIAL Source text by forcing all statements to begin in the same column independent of the statement number Thus syste matic alignment and i
9. initialized by AUTMAINT when an author is added to the system The on line system updates TERNHBS and NSESSIONS and uses ID It is possibie to completely remove AUTHREC from the on line system and froa the CHATJCL See the System Programmer s Banual under Suggestions for Future Work XINCLUDEd from DCLLIB ARECDEF JERR EES EAA EAE RE ERE ER okototetelokcclotokctoredoloketoiookokolotok EE EAE EEE EE AEE ERE 2 ID CHAR 9 RECORD KEY Author s id 2 NAME CHAR 24 2 PERSONNEL 3 PHONE CHAR 7 3 UNIV ADDBESS CHAB 20 2 DATE EST CHAR 5 Date this record added to AUTHREC 2 TERMHRS FIXED BIN 15 0 Number of terminal hours spent Form nnhn nn 2 NSESSIONS FIXED BIN 15 0 Number of successful sign ons accomplished by this author Figure 2 Nodel of an AUTHREC Record AREC 22 5 3 CALFILES THE HEART OP THE CAI SISTEN The most important of the on line datasets is CAIFILES The creation and saintenance of CAIFILES is described in Chapter 4 of the CAI Operations Manual CAIFILES is dec lared thus DECLARE CAIFILES FILE RECORD DIRECT UPDATE KEYED ENVIRONMENT REGIONAL 1 Note the disparity between the DD name CAI and the last qualifier of the dataset name CAIFILES this is the only file with that unfortunate quality In this manual it will be referred to by tae less ambiguous of the two names CAI FILES CAIFILES is a
10. it supported application programs written only in PL I F or S 360 Assembly Language However it has been modified fairly recently to accept programs compiled with the PL I Optimizing Compiler The source code accepted by the two compilers differs in a few ways Under the Optimizer internal procedures Bay not be declared ali builtin functions must be declared and some of the system functions have different names It may be advisable one day to generate a CAISYSTEM under the optimizing compiler IBM no longer offers programming support for PL I F The 1980 CAI System was built with the Optimizer in mind all builtins have been declared There fore to generate a CAI System under the PL I Optimizing Compiler do the following 1 Delete every declaration of an internal procedure in each of the source modules Most of the seventeen modules do not contain any such declarations 2 In the entry point STOP of module EQDQ replace the call to IHESARC with a call to PLIRETC Besides this the source code shouid not have to be changed although you may vant to take advantage of the DO amp s ED e als MAD SEP DEM MMC E D cam i n RR A aee 2 by Lee Nackman 50 UNTIL BEPEAT SELECT and LEAVE statements that are available with the Optimizer 3 Be compile all the modules using the Optimizer The options for compilation may have different names make sure the same options are in fact requested Moreover invoke the optimization
11. the OS routine which sets the task return code Hence the stop code is displayed to the user For an explanation of the stop codes and the smechan isa of STOP see Chapter 7 of this manual Other entry points in the nodule include INIT Called from CAIMAIN INIT defines all of the system resources and enggeues the system resource to lock out off line programs ENQ Called fron FILEIO to enqueue the first four regions of CAIFILES DEQ Called from FILEIO after writing on the first four regions of CAIFILES to dequeue EQEXT DQEXT Called from SNONOFF before after sign on sign off to engueue dequeue the student or author resources EQID DQID Called from SNONOFF before after Sign on sign off to enqueue dequeue a particular user id number 2 17 cc3010 This is the interface to the CHAT system input output routines as such it is the only module that needs to know about them All other routines merely address entry points of this module without actually talking to CHAT at all There are several entry points each of which serves a spe cial purpose 10 DISP and DSPURC display the given text on the current row designated by the external variable ROW the latter is also passed column information while the former begins the display in columa one of ROW RD_T and RD2_T read input from the CRT screen the former uses column information passed in as a param
12. 9 A Lesson s Conmpile Time Symbol Table 36 DCL 1 INSTNS BASED INS PTR OO OR e ele e ke ie oe o ok oko oe oe b b ole bdo EEE EEK RE obo o oko oko ERE EE This is what a page CAIFILES region of object code instructions looks like Delta machine instructions are single address each consists of an 8 bit opcode following by a two byte operand The instruction pages for each lesson are pointed to by that lesson s LCB For more information about Delta machine code and DIAL translation see Chapter of the System Programmer s Manual AINCLUDEd from DCLLiB INSTDEF x JERE ihe e ke o e e hoc HO MEE HE e joke kc k oec ok oko coke k ooo oko xo doloe sedeo xol ER ok RK ROKK 2 NEXT FREE FIXED BIN 15 0 The next free instruction location in OPCODE and OPND below Will be 513 i e signalling full for all but the last page of instructions filled by AUTHOR x 2 OPCODE 512 BIT 8 The opcode parts For a list of all opcodes and their y associated mnemonics see procedure CODEGEN 2 OPND 512 FIXED BIN 15 0 The operand parts 2 FILL CHAR 498 Not used exists only to bring the structure up to 2036 bytes the size of a CAIFILES region Figure 10 Template for a Block of DIAL Object Code 37 DCL 1 LIT BASED LIT PTE 9 EER EERE ke ok EE EK Joke kc ERR EEK EEE EEK EE ERE ooo EEE EE RAE IR
13. COURSE to check password information and by off line programs XINCLUDEd from DCLLIB MAINDEF J EEREREEREREE ode se ooo de joke eoe EERE EER EEE EEE AERA EERE ERE dotetoketel HK EEK ok LOGFILES x 2 LOGF COUNT FIXED BIN 15 0 How full is LOGFILES 2 LOGFILES 300 FIXED BIN 15 0 Each student has his own logfile A logfile is a chain of log records a logrecord is defined by the DCLLIB menber LOGRDEF A logfile is where the on line systems via the LOGGER module stores all of the lesson execution information which statements were executed and what responses were given by the student Each logrecord is held in a region on CAIFILES This array points to the first iogrecord of each logfile chain CHECKPOINT INFORMATION dihen a student signs on SNONOFF puts into HAINFILE the CAIFILES block number where his RESUME area SCB and his RECOVER area SCB are stored That way if the session ends abnormally they can be recovered the next time that student signs on If the session ends normally then SNONOFF stores the RESUME area in the student s SREC deletes his RECOVER area and removes from MAINFILE the pointers to them Another way to put it is that MAINPFILE CHECKPOINT lists all students ho are signed on right now plus all those whose last xy session terminated
14. Features are described which were never implemented and later features have been implemented which are not described in the dissertation A very important contribution to the CAI System would be made by the person who wrote such a manual 10 6 IHPROVING LESSON RE COMPILE TIME In his dissertation Mudge Chapter 8 offers a scheme for greatly reducing the time it takes for a lesson to re compiles Improving the recompile time involves a major Software change An incremental compiler would avoid producing a completely new object code file for each source code change by structuring the object code file as a chained list with each node being a set of object code instructions cor responding to one source code statement This would provide the important fast response to author changes It should be the next task under taken in improving the implementation of the CAI System Note however that such a chained struc ture can by introducing another ievel of indi rectness result in a slower execution So at say ATTACH time ail references should be resolved to absolute ones and the code linear ized so that the execution speed is equivalent to that of the directly compiled code in the cur rent implementation Some reprogramming of the current implementation could result in a language 68 processor closer in nature to the incremental compiler For example the system could make some ad hoc determination of which pa
15. PL C to Computer Science and Library Science students of UNC until the fall of 1978 The original course material was written by Dr Prederick P Brooks Jr 2 and has served as the curriculum of the systems adcapt f r Binor modification throughout the entire life of CAI here During its creation and testing the CAI system enjoyed the services of a systems programming team whose responsi bility it was to isolate and fix bugs in the new system a group of course proctors who oversaw the instruction pro cess aad ssoothed the way for the student users of the sys ten and a corps of students in several sections of program Bing courses sho learned from the system and evaluated its ease of use and effectiveness for Mudge and his colleagues CAI was a major effort of the Departrent Any large system will show sighs of age as time passes and the CAI system has been no exception By early 1979 it was only a ainor responsibility of the Department s software manager No one used it for instructional work or research at all The team originally responsible for its creation had long since graduated and the workstations fell into disrepair Chapter 2 DEFICIENCIES IN THE CAI SYSTEM Why did the CAI system fall from prominence into obscur ity For one thing the people who built it left For another it was always intended to be a research tool above all any production use it found would merely be a bonus Moreover one or t
16. Wortman D B A Compiler generator Prentice Hall Englewood Cliffs N J 1970 Mudge Jj Craig Human Factors in the Design of a Conputer assisted Instruction System Ph D Dissertation University of North Carolina at Chapel Hill 1973 Schultz Gary D The CHAT System An 05 360 MVT Time Sharing Subsystem for Displays and Teletype M S Thesis University of North Carolina at Chapel Hill 1973 73 lt LIST OF FIGURES 2 Figure 1 Model of a STUREC Record SREC a 2 Model of an AUTHREC Record AREC a a 3 MAINFILE Region 1 of CAIFILES a s 4 The Course Control Block Region 2 of CAIFILES 5 The Author Control Block Region 3 of CAIFILES 6 FBL TOP Region 4 of CAIFILES 7 FBL SEC Regions 5 10 of CAIFILES 8 Template for a Block of DIAL Source Code 9 A Lessoa s Compile Time Symbol Table a 10 Template for a Block of DIAL Object Code 11 Template for a Block of String Literals 12 Template for a Block of String Variable Storage 13 A Block of a Student s Log Information 14 A Student Control Block a s s a gt 15 A Lesson Control Block a 2 gt 74 Page LIST OF TABLES Tabie page esum
17. a new version of CAISYSTEM using the proce dures described in Chapter 3 The datasets used are 1 For CONSTRUCTOR UNC CS E557C CAI CONSTB with member XPLCONST for the XPL Constructor and member PLICONST for the PL I Constructor 2 The object module library UNC CS E557C CAI SYSLIB 3 For the XPL program UNC CS E557C CAI XPLOBJ The JCL is as follows Using XPLCONST JOB f f XPL EXEC PGM XPLCONST REGION 150K STEPLIB DD DSN UNC CS E557C CAI CONSTR DISP SHR PROGRAM DD DSN UNC CS E557C CAI XPLOBJ DISP SHR SYSPUNCH DD SYSOUT B DCB RECFH FB LRECL 80 BLKSIZE 5400 SYSPRINT DD SYSOUT A SYSIN DD LA mcd ue Using PLICONST A JOB STEPLIB SYSPRINT CONMENT DCLOUT INITOUT CODEGEN EXINPUT 74 EXEC PGM PLICONST REGION 300K DD DD DD DD DD DD DD DSN UNC CS E557C CAI CONSTR DISP SHR SYSOUT A SYSOUT B DCB RECFM FB LRECL 90 BLKSIZE 400 SYSOUT B DCB RECFM FB LRECL 80 BLKSIZE 400 SYSOUT B DCB RECFM FB LRECL 80 BLKSIZE 400 SYSOUT B DCB RECPN F B LRECL 80 BLKSIZE 400 54 Chapter 7 ABNORHAL TERMINATION CODES When a CHAT program in execution raises the ERROR condi tion CHAT displays a message of the form SUBTASK ENDED nnnn PLEASE CALL PROCTOR and then aborts the subtask The proctor reference is historical CHAT s original purpose was to provide a run time environment for CAI There are three forms the return
18. are reser ved They may not be used for any other pur pose 3 Setting the system variable CASE may be done only via CASEON and CASEOFF statements Setting CASE by assignment of integer value was never supported 4 Setting the system variable SQZ may be done either via the SQZON and SQZOFP statements or by assignment of an integer value Assigning zero to SQZ is equivalent to SOZOFF assigning any other value is equivalent to SQZONM 6 5 PROCTOR OVERRIDE FACILITY In student mode the proctor override facility can be used to jump to any lesson or to any Statement within a les son There is almost no on line diagnostic help with this facility in order to discourage student use of the facil ity The proctor enters pro 49 whereupon the system responds with a prospt The proctor enters ove lesson Or Jove line gt where the lesson name is entered to override to the begin ning of that lesson anda line number is entered to over ride to that line within the lesson currently being exe cuted If the override statement is invalid then the pro com mand must be entered to try again 6 6 OPEIEC The CHAT program OPEXEC may be used by a proctor to dis cover which CHAT terminals are in use how much core is cur rently available and many other things For more informa tion see the OPEXEC Description docusent 6 7 USING THE PL I OPTIMIZING COMPILER When CHAT was originally built
19. b The host operating environment for the CAI system was developed at roughly the same time by Gary Schultz 5 The CAI system runs under the Chapel Hill Alphanumeric Terminal CHAT system a single region resident time sharing monitor that runs under the 05 360 NYT operating system at UNC CHAT allows the interaction of sultiple application programs sith crt display stations aad provides input out pat pro gramming support for that interaction CAI is only one sub task application program that runs ia the CHAT environ ment others include a graphics interface package a text editor and a HASP monitor program CHAT was designed and built with one kiad of display terminal in sind a Computer Communications Incorporated CC 30 Communications Station This is a four color CRT with a lightpen anda forty char acter by twenty line screen In addition each terminal has a program controlied random access slide projector CHAT software includes support for controlling the projector and lightpen as well as reading and writing the CRT screen Mudge paid close attention to the working environment of his users and carefully designed special CAI workstations Each station consists of a CC 30 CRT and its keyboard lightpen slide projector anda desk type writing surface All of this is enclosed in an acoustically treated cubicle approximately six feet square The CAI system was put iato test production in 1972 aad was used to teach beginning
20. feature of the com piler the Optimizer does not optimize unless requested to do so 4 When the new System is generated it will have to be linked in with CHAT s PL I Optimizer interface as opposed to the PL I F interface currently linked in Consult the current CHAT expert to sake sure which CHAT dataset s to use 6 8 DEBUGGING AIDS This section deais with methods by which you can cause the CAI System to generate output elsewhere than on the user s display screen The CHAT system Raintains a log file where sign on and sign off information are stored for a limited period of tine To write to this log file use the CHAT routine LOGIT To use LOGIT declare it in each external procedure you expect will invoke it DECLARE LOGIT ENTRY CHARACTER VARYING when a new CAI System is generated LOGIT will be known because it resides in the CHAT SYSLIB To invoke LOGIT call it with a character string To see the results sign on to OPEXEC under CHAT and enter the command SHO LOG Your message should appear Be warned however that dis playing the log file also clears it Aliso the file is not very large Writing many messages to the file will cause earlier messages to be lost Therefore it is advisable to display the file freguently Another way to obtain output fron the system is to include a print file in the system The most convenient file to use is the system print file SYSPRINT However it is more convenient to d
21. is being executed for this student Encoded in the IC is the instruction page and the offset within the page Special values of IC are Ic 0 Student has not yet started into a course thus SCB LESSON is meaningless IC 513 Execution is at Instruction 1 in SCB LESSON IC lt 0 Student has finished SCB LESSON he should begin the next session at the start his course s next lesson 7 2 PAUSE LEN FIXED BIN 15 0 How iong in seconds will the system pause between SHOWS Set by the PAUSE lt n DIAL statement 2 UNREC_CTR FIXED BIN 15 0 How many unrecognized re sponses to a SHOW have been received This is used to process the DIAL U NBEC statement to control branching 2 STATES AIO oak doe ol X d E ce ok OR Current states of this student s Delta machine xs OBEROI IIE ARIE IDI IO JO IAGO OI TAO 7 lt 4 3 READ ISSUED BIT 1 3 SHOW UP BIT 1 3 CASE BIT 1 Translate alphabetic case Set by DIAL CASEON CASEOFPF stmts 3 SQZ BIT 1 Squeeze blanks from a response P Set by SQZON SQZOFF stmts 3 cc BIT 1 Condition code set by some DIAL instructions tested by others 2 STORAGE Sab ck e dei co e e geo e de c eec eae ke ERE EEE EERE EKER EERE EE EERE EK Run time storage for variabies Instructions with operand type 2 3 reference this ar
22. is now under development it is called CHATHP A CAI System may be generated to run under CHATHP Since the CHAT interface appears only in the CC30I0 module only that module will have to be changed Re compile that module according to the following JCL and then generate the full or student only system as usual as shown above jobname JOB acct name T 2 H 200K Li EXEC PLECL PARM C M PARM L XREF LIST NCAL C SYSLIB DD DISP SHR DSN UNC CS E557C CHAT SOURCE C CHATSRC DD DISP SHR DSN UNC CS E557C CHAT SOURCE Z C SISIN DD DSN U NC CS E557C CAI SOURCE 4 CC301IO DISP SHR L SYSLIB DD DISP SHE DSN UNC CS E557C CHAT PLILIB DD DISP SHR DSN UNC CS E557C CHAT SYSLIB i DD DISP SHR DSN SYS1 PLILIB L SYSLHOD DD DISP SHR DSN UNC CS E557C CAI SYSLIB VOL L SYSIN DD INCLUDE SYSLIB HPNTRYS NAME CCJOIO R PEA The generated system should run on the HP terminals Now all is not automatically well The HP terminals have a larger screen than the CC 30 s and all of CAI expects a CC 30 screen Messages are formatted with that in mind and variables such as THRON LIM ROW COL etc are set accordingly Until the CAI System can be rewritten for CHATHP try reducing the screen size on the HP s by using the margin setting and memory iock features However the CHATHP version should also run as usual on the CC 30 terminalis 15 Chapter 4 THE TRANSLATION AND EXECUTION OF DIAL CODE The main purpose of the CAI
23. some of the off line utilities programs and by the on line student file inspector CAIOLFI INCLUDED from DCLLIB SRECDEF f R0 ke e oe doc oec o EKER HEE oic c EERE BEE REE AR EE occeolokoketoketooleketekoteteteotekeetelolekek STUDENT RECORD OR koe EEK ooo olo KEE E EEE EE ERRER ERE EEE E HERR EEE EEE EE EAE EK EAE ERE PART I Bureaucratic information about the student The data that does not change from session to session e g name id creation date etc was put here by the off line utility program STUMAINT The rest is updated by the on line system See the Operations Nanual to learn about STUMAINT VARLIER ERE BER EEG EK BAEK oko ok EAE ER EER ERR EE EEEE E E S EEE EE E ESEESE EERE REE KEY Student s id number 2 2 2 ID CHAB 9 NAME CHAR 24 PERSONNEL 3 PHONE CHAR 7 3 YEAR CHAR 1 3 MAJOR CHAR 4 3 UNC COUBSE CHAR 9 DATE CHAR 6 TERMHRS FIXED BIN 15 0 19 the file s record key 1 G or F faculty Format standard UNC department abbreviation e g COMP Format AAAABBBBN where AAAAS standard UNC dept abbreviation BBBB course number right justified and Nt the section number For exaBpie COMP 161 stands for COMP 16 Section 1 Date this record was created format YYMMDD Number of terminal hours this studen
24. the production courses in the CAI System In particular it lists all the course names the number and names of each course s lessons and in which block of CAIFILES the LCB for each lesson is stored The CCB can hoid information for up 40 courses and 2048 associated lessons XAINCLUDEd from DCLLIB CCBDEF J BERR e ab jede c oj eje oie kot e a o e ob t eo nj cibo d de HKG EEK EEE EERE EERE 2 COUNT FIXED BIN 15 0 Number of courses currently in the CAI System 2 NEXT FREE FIXED BIN 15 0 The next free element in CCB RECS So NEXT_FREE 1 is the nbr of lessons in the CCB 2 COURSES 40 8796 8E e ce KIA c e hp sp p EE kc ee ie d epo EE oe ERE EE EEE EEE RRR EERE E E For the i th course CCB COURSE i holds the name of that co rse the number of lessons comprising it and the index in CCB BECS of the information about its first lesson fk le hook dee jc lobe es d e e jojo e oleo dede doloe ESETET EEEE ETE TEET ETTET N 3 COURSE ID CHAR 6 The name o the course 3 REC INDEX FIXED BIN 15 0 Index of this course s first lesson s data in CCB RECS 3 REC LEN FIXED BIN 15 0 Number of lessons in this course 2 RECS 204 fF OE Xo eo 3 3 se ci pe oe e e e e KK ac o e o E A ao ale xo RK RE KEE ERE ak KH EEE For each lesson of each course CCB RECS holds the lesson name and the block number of CAIFILES where th
25. the references to CAI in the CHATJCL des cribed above Traditionally the lines have not actually been taken out but merely transformed into JCL comments In this way restoration of CAI in the CHATJCL is quite simple 4 2a 3 6 3 Move the files to off line disk packs Since CHATJCL CAI TEST is only for test versions of the on line system it may be possible to delete it completely provided there are no load modules resid ing therein that warrant preservation This dataset is often reduced in size to one track in lieu of actual deletion Follow the wrap up procedures outlined in Section 7 2 2 of the CAI Operations Manual AUTHOR COMMAND FACILITIES The author command facilities are described in Section 5 5 of Mudge s dissertation The following addenda now apply 1 Only the first three letters of any command ate sig nificant The command may be entered in upper and or lower case letters The include command was never iBplemented Hence neither was group The course author command was never implemented it was instead built as an independent on line CHAT pro gran The number command was renamed It is now line The reseguence command was renamed It is now renunmber The print command was never implemented but there is an off line PRINT progran It is described in Section 7 1 of the CAI Operations Manual There is a csw command which flips the COHPILE Switch on and off This
26. the sys tem removing lessons from a course creating or removing a course and displaying formatted information about the con tents or available space on the files The directory or information requests could offer a print option causing a print job to be submitted to the batch job stream 26 Implementing such a system would not be very difficult as programs already exist which perform each transaction listed above The print option has been implemented in another CHAT application seogtan and so that logic is also available Finally such a system could employ some of the modules of the on line CAI system such as the main driver the input output interface module and the module which updates the author directory with very little if any modification 097 BIBLIOGRAPHY Barrier Jack Clements Paul C and Mudge J Craig UNC CAI System Programmer s Manual University of North Carolina at Chapel Hill 1980 Brooks Frederick P Lessons on PLC programming written for the UNC CAI system 1973 Mudge J Craig Human Factors in the Design of a Computer assisted Instruction System Ph D Dissertation University of North Carolina at Chapel Hill 1973 Mudge J Craig On Writing Reentrant Programs in PL I SACM Newsietter a Publication of the University of North Carolina Student Chapter of the Association of Computing Machinery Chapel Hill November 1971 2 3 Schultz Gary D The CHAT System An 05 360
27. your lesson Experi ment with color displays the DIAL pattern matching facility the SQZ and CASE system variables di CONTENTS iii USING THIS MANUAL 2 o gt gt gt o e o ili PREFACE Chapter page 1 OVERVIEW OF THE CAI SYSTEM a ao e o oo 1 2 THE EXTERNAL PROCEDURES CONSTITUTING THE CAI SYSTEM 3 CAIMAIN 1 Ll a x L 9 bd 3 SNONOFF LJ s 2 a a bd 3 FULLCAI a 2 E o 7 Ld 4 STUONLY a 2 w Ld w t 5 AUTHOR a D 5 ACBPROC 2 s s 2 gt kad a 5 COMPLER gt a o a s e 4 o 4 ww x w e s E 6 TABLES a gt s Ld 2 o a 6 CODEGEN a a a 6 SOURCE Eod LJ D a 2 LJ o 7 ERECTOR amp e 4 ue d oco Se ie ee ae m tay Se me OB PATPROC L gt w 2 kad 8 LOGGER e 2 e gt a a a Ld Ld Ld 1 8 FILEIO gt a 9 ALLOTOR 2 gt Ld head Ld gt gt gt bad es 9 EQD0 Ed Ld L 10 CC30IO 2 v 9 gt gt v LJ gt 10 3 CAI SYSTEM GENERATION e a a o s s we we sa 12 Generating the Full Systen CAIAUTH e e 13 Generati
28. 1 of recompiling an error was found in a DIAL statement DIAL system error S LEN of a statement is 1 or 5800 Called fron GSOURCE When ENDing on a CAIFILES resource the Subtask already had control of it When DEQing on a CAIFILES resource the subtask did not have control of it Called to read with BLK 1 Called to write with BLK lt 1 Called to rewrite with BLK lt 1 Called to read with BLK gt 1899 Called to write with BLK gt 1499 Called to rewrite with BLK gt 1499 Attempt to allocate block numbered higher than 1499 no more blocks on FREE BLOCK LIST some must be freed In Stage 1 of recompiling GSOURCE returned a nonzero return code Stack cannot be shifted down any more Software error caused by returning sore blocks than allocated Bottom of stack on free block list has been reached Attempt to DEQ on STUDENT resource 57 55 SNONOFF 56 SNONOFF 60 EXECTOR 99 CAIMAIN not successful Attenpt to DEQ on AUTHOR resource not successful Attempt to DEQ on a sign on ID was not successful read pen or read either instruction was encountered in a system without lightpen capabilities l ON CONDITION ABNORM signalled more than 10 times 58 Chapter 8 PROTECTION OP CAISYSTES DATASETS CAISYSTEM lives and dies with its files Great care must be taken that all datasets are protected from system fail ure CAISYSTEM bugs and acts of God Precautions fall into t
29. ADER INIT EQEXT DQEXT Reference Section 2 4 1 STUREST restores students BECOYNEEDED bits as appropriate after loss of file STUREC XINCLUDEd members SRECDEF MAINDEF EQBQEXT Procedures called HEADER INIT EQEXT DQEXT Reference Section 6 2 64 9 3 HON PRODUCTION OFF LINE UTILITIES The following utilities are not considered to be ready for production use They are not tested or not fully implerented some should never in fact have to be used at ali No load modules for these programs exist 1 ACCESS prints all password protected programs and their associated passwords INCLUDEd members MAINDEF Reference Section 4 4 3 2 AUTHINIT a one shot initialization program for the ISAM file AUTHREC Should never have to be used again The source code is Oobsoiete and should be used as a model only should the file ever need to be recreated DO NOT EXECUTE THIS PROGRAM 3 CAIINIT a one shot initialization program for file CAIFILES Should never have to be used again The version in the UTILITY SOURCE dataset is obsolete and is retained for historical purposes only in case another one should have to be written DO NOT EXE CUTE THIS PROGRAM Reference Section 4 2 4 STUINIT a one shot initialization program for the ISAM file STUREC Should never have to be used again in fact the retained source code is obsolete Serving only as a procedural model should STUREC ever have to be r
30. AE OE EK This is what a page CAIFILES block of object code character string literals looks like The literals pages for a lesson are pointed to by the lesson s LCB SINCLUDEd from DCLLIB LITDEF fS Ookokoke Roe de ko A A a dololok oce leoketotokookoetekolkodokcdotoedoleloioekekototolokojoke loeo 2 NEXT FREE FIXED BIN 15 0 The next free location in LIT DATA Used by AUTHOR when adding a literal to this page from TEMP TEMP LIT 2 DATA CHARACTER 2034 The actual character string lit erals for this page Each literal begins with two bytes of length information and a two byte header containing START COL screen formatting information for DIAL SHOWAS statements at execution time The length then is the length of the literal plus two The START COL information is used by the lexical SCAN routine in COMPLER and by EXECTOR Figure 11 Template for a Block of String Literals 38 DECLARE 1 POOLI BASED PL1_PTR J EREREEEEKEEE dide ded d b ENE EE eoo e oe GEER Xo e d ERD eee REESE KEK POOL1 is the first half of the run time storage for DIAL character string variables The lengths and pointers of to each string are held in SCB STORAGE S PTR The second half of the run time string variable storage is POOL2 Each of POOL1 and POOL2 is the size of a region of CAIFILES Together with SCB they make u
31. DD DISP SHB DSN UNC CS E557C CAI SYSLIB L SYSIN DD INCLUDE OLDNOD SNONOFF INCLUDE OLDMOD EXECTOR INCLUDE OLDMOD CAIMAIN INCLUDE OLDMOD CC3O0IO INCLUDE OLDHOD LOGGER INCLUDE OLDMOD ALLOTOR INCLUDE OLDMOD FILEIO INCLUDE OLDMOD PATPROC INCLUDE OLDMNOD EQDQ INCLUDE OLDMOD STUONLY LIBRARY AUTHOR ENTRY IHENTBRY NAME CAI B 4 3 3 NOTES CONCERNING SISTEN GENERATION The OLDMOD DD line points to the PDS where the object modules for the source routines are stored The SYSLMOD dataset is where the load module for the generated system will go Note that there is another dataset reserved for test versions of the CAI System you may want the load module to go there That dataset is UNC CS E557C CHATJCL CAI TEST The NAME command in the linker input specifies the member name given to the load module and it is this name that must be given when signing on under CHAT in order to invoke that load module The 18 R specifies that if a member with the given name already exists it is to be written over with the new load module If B is not specified and a member with the given name already exists then the linker stores the load module in member TEMPNAME unless a member already exists with that name in which case the job step fails 3 4 GENERATING A SYSTEM TO RUN UNDER CHATHP A version of CHAT that will allow its application pro grams to run either on the CC 30 or the Hewlett Packard ter minals
32. E E E a E E EL a EEE EEE 2 COUNT FIXED BIN 15 0 Number of authors currently known by the system how full ACB AUTHORS is 2 NEXT FREE FIXED BIN 15 0 Next free element in ACB RECS NEXT FREE 1 is the total number of unattached lessons in all authors libraries 2 AUTHORS 40 Each instance of ACB AUTHORS holds a particular author s id number the index in ACB RECS of information about that author s first lesson and the number of lessons that the currently has in his library un attached to courses 3 AUTH ID CHAR 9 3 REC INDEX FIXED BIN 15 0 INDEX OF AUTHOR S FIRST LESSON 1N RECS 3 REC_LEN FIXED BIN 15 0 How many unattached lessons this author has in his library 2 RECS 184 Each instance of ACB RECS holds a lesson name and the biock number in CAIFILES of that lesson s Lesson Control Block ys 3 LESSON CHAR 6 The lesson name 3 LCB FIXED BIN 15 0 Block number of the LCB for this lesson JS ERE bk jede kk o ce oh ERE AEE ER EEE RAE EERE ERE I dolootokek For instance Author i s id is in ACB AUTHORS i AUTH ID x He has ACB AUTHOBS i REC LEN lessons in his library The x7 LCB for tae first one is held on the CAIFILES block specified ACB RECS ACB AUTHORS i REC INDEX LCB The LCB for the j th one is in ACB RECS ACB AUTHORS i REC INDEX j 1 LCB There i
33. EAE ER tetoteoloek 1 C SYM DOPE BASED C SYM D PTR Joe e oe i de i oie jc ke e ot ke db o oh EK KKH KK 2 TYPE 339 FIXED BIN 15 0 Explained in the following Type 2 ADDR 339 FIXED BIN 15 0 Definition Table SERR kkk EEE KES ERECT E KEE EKEAERK EK x TYPE MEANING CONTENTS OF ADDR PUT THERE BY L mm LmI mIlc mmpL LXLIDEGIILMIEIDEELLALLLILILLI mIm ImiI uI u IummI 0 Undefined jo i i r 1 Character string SCB STORAGE S_PTR CODEGEN lt DCL ST i variable i index or default i i i i i 7 i i i 4 2 CCNAME Address in LIT an jCODEGEN lt DCL ST i i i i i i i encoding of page using ABSOLUTE i and offset NEXT LIT i gt i i 3 CHAR STR CONST i a i i i 4 jInteger variable SCB STORAGE INT index CODEGEN lt DCL ST i 5S jInteger constant se i i i i 6 Slide variable SCB STOBAGE INT index 4CODEGEN lt DCL ST i i i 7 Slide Constant jActual value ICODEGEN lt DCL ST y i SC i i i i i 8 not used ji i 35 i i i 9 Label Branch address in CODEGEN lt LABEL gt i INSTNS encoding of l i page and offset x i i i x 10 jLabel needing iPointer to last ele CODEGEN when i fixup ment added to the orward branch 1 fixup chain j situation
34. FI enhanced to include author file inspection then AUTHREC would have to remain online in the CHATJCL however it still seems like a streamlining to take it out of the CAI System 10 2 REJUVENATING THE CAI OPERATIONS MANUAL The text for the CAI Operations Manual currently resides on a disk dataset in the form of Hypertext input Since Hypertext is no longer available at UNC an effort should be made to convert the manual to a form acceptable to a current text formatter The easiest candidate might be TEXT360 However by using a text editor conversion to any other formatter e g FORMAT SCRIPT might not be too difficult Once that is done a comprehensive update is in order The Operations Manual is generally complete and well written but many details are outdated For instance many dataset hames have been changed over the years and the JCL given for some jobs has changed slightly At this writing there is one copy of the Operations Manual that has been updated by hand to reflect all such changes This was done during the development of the 1980 CAI System The Department s Facilities Manager should know where that annotated manual is it is clearly marked as the updated version In the back of the updated Operations Manual is a hand written manual of class start up procedures It was written apparently hastily by someone on the original CAI team and should one day be enhanced and text formatted Such a manual could and undou
35. HO O RENOVATION OF THE UNC CAI SYSTEM by Paul C Clements Thesis submitted to the faculty of the University of North Carolina at Chapel Hill in partial fultrillment of the reguirements for the degree of Master of Science in the Department of Computer Science Chapel Hill 1980 Ap ed by Nep Adviser PAUL CHARLES CLENENTS A Renovation of the UNC CAI System Under the direction of Peter Calingaert This thesis describes work undertaken to modify the Com puter Assisted Instruction systems at the University of North Carolina at Chapel Hill The modifications include enhanced internal documentation of the PL I source code and re Structuring of local code sections to eliminate confusing branches The architecture of the system has been changed by deleting the lightpen feature ceplaciag its functions with keyboard commands color codiag of system information and warning gessages and the inp Yonsatation in the author language of integer subtraction Suggestions for future work are offered The new System Prograsmer s Nanual is attached as an appendix to this docuszent i TABLE OF CONTENTS Chapter page 1 INTRODUCTION e o oe ee cess sero 1 2 DEFICIENCIES IN THE CAI SYSTEM ec 2 2 5 3 THE MODIFICATIONS UNDERTAKEN oo o oo oo o 12 4 SUGGESTIONS FOR FUTURE DEVELOPMENT o e o o o o a 23 Appendix page Aw CAL SYSTEM PRO GRAMMER S MANUAL a a 4 o o a gt s D 29
36. I system serves asa shining tribute by counterexasple to the doctrines of structured programming Chapter 3 THE MODIFICATIONS UNDERTAKEN My work on the CAI system was divided into two catego ries architectural modifications which will be visible to the production user of the system and modifications which will be visible only to a CAI system programmer Included in the latter category are the enhancement of internal documentation restructuring of local code sec tions and the completion of the System Programmer s Manual The internal documentation that I supplied to the modules consisted of enhanced header paragraphs as well as in line comments The header documentation for each module followed the same format and consisted of the foliowing information 1 Function This is a general prose definition of what the particuiar module is supposed to do Because of the nebulous nature of each module s task this information is necessarily imprecise It is meant to give a program mer who is searching for the cause of a problem a good idea of which module to pay special attention to In a few cases I was able to use descriptions that already existed provided by the original CAI programming team 2 3 4 3 Parameters This is a list of the parameters for this module with a brief description of the information car ried by each Included is whether the parameter is given that is its value is set externally
37. ILES ALLOTOR keeps track of which regions are currently iu use and which are currently free by maintaining the Free Block List There are 1499 regions on CAIFILES region 1 holds MAINFILE region 2 hoids the Course Control Block CCB and region 3 holds the Author Control Block ACB The Free Block List FBL itself occupies regions 4 through 10 of the file Ali of the other regions 11 through 1499 are coatrolled by ALLOTOR ALLOTOR can either claim a free block for user by the calliag procedure thus removing its number from the FBL or return a no longer needed block to the FBL For an expianation about the mechanism of the FBL see the declarations for the structures FBL TOP and FBL_SEC illustrated in Figures 6 and 7 of this manual 2 16 BOD0 This routine issues calls to ENQ and DEQ which are CHAT routines that provide a PL I interface to the OS ENQ DEQ supervisor sacros EQDQ also maintains the status of each of the serially reusable resources whose use is being con trolled For an explanation about the Systen s serially reusable resources and the enqueue and dequeue protocol see Section 8 1 of this manual The most heavily used entry point of this rodule is the STOP routine STOP is called when the system discovers an error condition with which it can t cope For instance if the CAIPILES Free Block List empties ALLOTOR cails STOP Each caller supplies its own stop code which STOP passes on to IHESARC
38. MVT Time Sharing Subsystem for Displays and Teletype Master s Thesis University of North Carolina at Chapel Hill 1973 Sneeringer James More on Writing Reentrant Programs in PL I SACH Newsletter a Publication of the University of North Carolina Student Chapter of the Association of Computing Machinery Chapel Hill December 1971 5 7 28 Appendix A CAI SYSTEM PROGRAMMEB S MANUAL 29 PREFACE USING THIS MANUAL This manual is intended for anyone engaging in modifica tion documentation enhancement or maintenance of the UNC CAI System A user of this manual shouid already have per formed the following 1 be Read the CAI Operations Manual written by Mitcheli J Bassman this gives an overall view of the files ased by CAI and the atility programs which exist to maintain then Read chapters 4 and 5 of Human Factors in the Design of a Computer Assisted Instruction Systen by J Craig Mudge These chapters explaia the architec ture of the DIAL programming language and the opera tional environment of the CAI system Become familiar with CHAT and the CC 30 terminals Become familiar with the CAI system Using the file procedures listed in the Operations Nanual enter yourself as a student into the systen and then go through some of the course material in student mode Enter yourself as an author in the system and write a seali instructional lesson in DIAL Explore the author commands Try executing
39. OFF SNONOFF EXECTOR EXEC TOR SNONOFF ACBPROC ACBPROC CODEGEN CODEGEN COMPLER AUTHOR AUTHOR SOURCE SOURCE SOURCE SOURCE AUTHOR EXECTOR EXECTOR LOGGER EXECTOR CA MAIN CODEGEN CODEGEN TABLE 1 Table of STOP Codes During recover phase the student s checkpoint entry was not found on MAINFILE during signon Student s checkpoint entry was not found on MAINFILB during sign off During setup for student execution course was not found on the CCB During setup for student execution lesson was not found on the CCB While setting up student s checkpoint entries on MAINFILE no room was found CHP COUNT gt 50 Author s iD not found on the ACB No room left in RECS NEXT FREE 184 No room left in STOBAGE S PTR called from internal procedure S ALLOC No room left in TEMP INSTNS called from internal procedure EMIT Symbol table fuil Called from internal procedure SCAN No LIT pages left more than 16 used No INSTNS pages left over 654 used No room left on source code file for a Split No room left on source code file while adding sequentially Statement number not found in first level directory called fron ASOURCE Statement number not found in second level directory calied from ASOURCE No room left on CCB to do an ATTACH During change of lesson lesson name not found on the CCB Duriag change of lesson no more lessons found for this course During open operation no room in l
40. STUREC is an ISAM dataset containing student enrollment records For a description of the creation and maintenance of this file consult Chapter 2 of the CAI Operations Manual STUREC is declared thus DECLARE STUREC FILE RECORD KEYED UPDATE DIRECT ENVIRONMENT INDEXED 5 Input output is by the usual PL I statements READ FILE STUREC INTO structure name KEY STU ID WRITE PILE STUREC PRON structure name KEYFROM STU ID The records in file STUREC are instances of the PL I structure SREC STUREC contains all pertinent student per sonal data and CAI status See Figure 1 for a complete des cription of the record format of the STUREC file T8 DECLARE f X olco ek de dede ER obe e joke ook EERE HEE EEK ERAGE e coelo olo EK EH KEK ER ERA EAE SREC is what one record on the ISAM file CAI STUREC looks like 1 SREC CONTROLLED It contains everything there is to know about a particular stu dent in the CAI System In particular SREC is composed of two major kinds of information The part consists of all the bureaucratic information available name address course etc The second is the copy of the student s Delta machine activation record which is stored on SREC between sessions and used to create the on line in core activation record at sign on SREC is used in the on line CAI System only by SNONOFF since it s the only module that accesses the ISAM files It is also used by
41. SYSTEM is to provide a pro gramming system for the DIAL language This chapter is intended to give the internal representations of source and object code for DIAL programs and to explain the relation Ships among the AUTHOR COMPLER and EXECTOR routines Oversimplified the relationship is this COMPLER trans lates into object code the single DIAL source statement given to it by AUTHOR the object code is later executed by EXECTOR The object code generated by COMPLER is not System 360 machine code but an intermediate form which Mudge chose to call Delta code This Delta code is executed by EXECTOR Thus EXECTOB can be thought of as an implementation of a Delta machine This machine has a single address instruc tion format each iastruction consists only of an eight bit opcode followed by a two byte operand instructions are paged by the Delta machine Character string read only literals addressed by Delta machine instructions are also paged Thus object code consists of a set of instruction pages a set of literal pages and the associated page translation tables For an explanation of the object code instruction set see the CODEGEN module especially the section where the opcode mnemonic variables are declared The object code is reentrant allowing for sultiple stu dent execution of the same copy of a lesson student s activation record contains his current Delta machine status including state definitions and reg
42. UTHOR and returns AUTHOR then dis piays the diagnostic and the offending statement and reads the author s correction If COMPLER does not find an error it reports that all is well and AUTHOR prompts the user for another command or DIAL statement Now for each DIAL statement that AUTHOR receives from the user it passes that statement to CONPLER along with the current symbol table COMPLER operates on that statement only emitting its object code into TEMP_INSTNS and TEMP LIT On return if no error has been detected AUTHOR does the following 1 adds TENP INSTNS to the end of the file of INSTNS pages 2 adds TEMP LIT to the end of the file of LIT pages 3 adds the source statement to the end of the source code file 4 performs housekeeping e g fixing up forward refer ence chains in the file of INSTNS 5 saves all the foregoing on their respective disk files 17 Chapter 5 CAI SYSTEM DISK INPUT OUTPUT There are three on line disk files used by the CAI System during a session Two are ISAM files and contain student and author directories respectively The third is a direct access file containing everything else all the LCB s the source and object code files the SCB s etc The ISAM files are accessed only by the SNONOFF routine at sign on or sign off During the rest of the session only the direct access file with its muck faster access method is ever used 5 1 STUREC THE STUDENT RECORD FILE
43. abnormally 2 CHP COUNT FIXED BIN 15 0 How many students have checkpoint information in MAINFILES right now 2 CHECKPOINT 50 3 STU ID CHARACTER 9 This student s id nbr 3 RECOV FIXED BIN 15 0 Block number of this xy student s RECOVER area SCB copy 3 RESUM FIXED BIN 15 0 Block number of this 7 student s RESUME area SCB copy LOG OF PASSWORD ACCESSES This log is cleared by running the off line program ACCSLOG See CAI Operations Hanual for details 2 ACC COUNT FIXED BIN 15 0 How many accesses now stored 2 ACCESS LOG 37 24 3 ID CHAR 9 who wade the restricted access 3 PGN CHAR 8 What program was accessed PASSWORD ACCESS KEYS 2 FILE ACCESS 9 Room to store 9 restricted pgm nanes and their associated password keys 3 PGM CHAR 8 3 KEY CHAR 3 DALTLY JOB COMMAND VECTOR 2 DJICONV BIT 16 See CAI Operations Manual for explanation especially sections about the CAILOG and DJCVMNT utility programs Figure 3 MAINFILE Region 1 of CAIFILES 25 DCL 1 CCB BASED CCB PTR fS oko Reo deo REI EEE EK EK EGE BEE EEE EERE EEE E E E EEE E E Z EEE EE ERA EE This is the Course Control Block held on Region 2 of file CAL CAI CAIFILES CHATJCL Like all blocks on CAIFILES it is 2036 bytes long The CCB contains information about all of
44. and only used here returned its value is set in this module to be used externally or both Input This is a specific description of what input this moduie expects By input I mean input from the user or input from the CAI dE files not input through parameters from other nodules There is an exception to this distinction however The CAI system has a module called FILEIO iie purpose of which is to read and write one of the system fiies parameter is the information to be transmitted A call to this procedure has the same effect as performing file input output therefore in the interest of providing more complete information I have used the Input paragraph in many cases to describe such calls However I was careful to make it clear in each case that I was in fact describing the effect of a cxi to FILEIO and not real input Output Similarly this describes what output this module generates for the user or onto the files Functions called This is a list of all of the proce dures called by this module with a brief decription of the task of each Internal procedures are differentiated from external procedures but both are described 6 References For those modules where external sources of information may be helpful such sources are cited 7 Compilation information Designed to help bring about a successful compilation and linking of this module this section gives a complete transcript of the necessary JCL includin
45. and provides information about a given student s file status There is currently no external documentation about this program but it is well emgineered and its use should be seif explanatory Unfortunately it depends on user input th rough a lightpen and so its use is restricted to those cCC 30 terminals with a functioning lightpen The third on line system is that which is described in Mudge s dissertation and exists in two forms CAI of CAIAUTH The former is for student use it presents lesson material analyzes responses and logs progress The latter does all of that as well but it also supports the author environment of the syster The source handler compiler and code generator for DIAL statements are contained here as is the large module which serves as the interface between an a thor and the system Over the years some specialized terminology has sprung up Which bears explaining The term CAISYSTEM refers to all of the production programs having to do with CAI at UNC HM a 4A AB DR al ee ee cae VOIR cu c e There is in fact a small set of hybrid routines that may be executed either from a batch program or called by an on line program these will be pointed out and described in Section 9 2 this includes on line and off line routines On the other hand the CAI System typically refers to either the CAI or CATAUTH on line programs This manual deals primarily with the CAI Systen The other on line programs and the
46. at lesson s LCB is stored The lessons are grouped together by course S0 Robe hohe eee o o ak aa tolok HEE EE AEE deotoketokeloketotokololelekelek 3 LESSON CHAR 6 Name of this lesson 3 LCB FIXED BIN 15 0 Block nbr of this lesson s LCB J SR ok de bee bee ook lo doe ek ERIE EA ooo olo eek ook EEE EEE EEEE For example the CCB can hold information about 40 COUNT more courses and 204 NEXT FREE 1 more lessons The LCB for the first lesson of course i is held in the block of CAIFILES given by CCB RECS COURSES i REC INDEX LCB The LCB block for the j th lesson of course fi is given by CCB RECS CCB COURSES i REC INDEX j 1 LCB The i th course has CCB COURSES i REC LEN lessons attached a 25 f 88 e ot e oe b d e he ceto e e d ele dee c b e aee oe dee eie odo c o kc i ee kak k o oe EK Figure 4 The Course Control Block Region 2 of CAIFILES DCL 1 ACB BASED ACB_PTR J Soo a koe ERE EREEEERE EERE de oto EEE EEE EK EEE EE EE EEE AREA KES BE EERERE AUTHOR CONTROL BLOCK Held on Region 3 of CAIFILES this structure gives status information about all autaors known to the system Basically it is a list of all authors with information about where all the LCB s are for the lessons x currently in each one s library XINCLUDBd from DCLLIB ACBDEF f Solo ole cook EERE AE REE RENE EER EERE ER EE T E EE S ES EE EE
47. bit controls whether or not the lesson is recompiled each time an out of sequence Statement is entered This command replaces the lightpen button C described in Mudge The SUBST and THROW lightpen commands do not exist The THROW feature was replaced with a key board command cle which gives the author a clear Screen on which to enter the next presumably long DIAL statement 48 9 There exists a copy command which lets one author bring a copy of another author s lesson into his own library The syntax is COPY lt author id gt lesson name where author id is the sign on identification of the author whose lesson is to be copied and lt lesson name gt is the name of the lesson to be copied 10 There is an edit command which allows the author to specify the row on which he wishes to enter input This is meant to allow an author to make changes to a lesson by listing the lesson and making the changes directly to the affected lines rather than having to re type entire statements 6 5 ADDENDA TO IHE DIAL SPECIFICATIONS The author language described in Chapter 4 of Mudge is not quite the author language that Was actually implemented in the CAI System 1 The following features are not implemented FRAME SUBSTR LENGTH INDEX PLISUB procedures vectors IF THEN IF THEN ELSE and DO WHILE Default branch ing for a MATCH statement is not implemented 2 Ail DIAL keywords and their abbreviations
48. bject modules is not impor tant with one exception The module TABLES must appear in the list before the module COMPLER The reason is that TABLES initializes certain COHPLER data structures declar ing them STATIC EXTERNAL INITIAL The COMPLER module knows them as STATIC EXTERNAL and so the linker must be given the initialized variable references first The load module created by this procedure takes about fourteen tracks of a 3330 disk volume T3 3 2 GENERATING THE STUDENT ONLY VERSION CAI The procedure for generating the student only version of the system follows Notice that the AUTHOR COMPLER CODE GEN ACBPROC SOURCE and TABLES modules are not included this results ina dramatic savings in the amount of core required Because the system makes extensive use of dynamic storage ailocation measurements of the run time memory reguirement are necessarily isprecise However the author version of the system requires approximately 226K while the student only version uses only about 134K The LET option and the LIBRARY statement promise the linker that AUTHOR and hence the other omitted procedures will never be called jobname JOB account name pargzs Pl passuord PEA EXEC PLFLD PABH L XREF LIST RENT LET L SYSLIB DD DISP SHR DSN UNC CS ESSTC CHAT PLILIB ff DD DISP SHB DSN UNC CS E557C CHAT SYSLIB DD DISP SHR DSN SYS7 PLULIB L SYSLMOD DD DISP SHB DSN UNC CS E557C CHATJCL CAI LOADLIB VOL L OLDMOD
49. block Figure 8 Template for a Block of DIAL Source Code 38 DECLARE 1c SYM BCD BASED C SYM B PTR BRE oO E ojo kc ode doe doe EE EEE c o cce ooo oc okoloke EGE jo EI ER ERE REE EER EERE EEE C SYM BCD is the first half of the compile time symbol table for this lesson The second part is C SYM DOPE This part is just a list of the identifiers currrently in the table all information about them is contained in the other part When not in core each instance of C SYM BCD resides on a region of CAIPILES pointed to by the lesson s LCB The index of an identifier in C SYMH BCD is also its index in C_SYM_DOPE AINCLUDEd from DCLLIB SYMBDEF ff 890 dod ooo ke ok EERE koc EEE coo kc EREEEAR ERE EAE AREA EEE ERE EE REE EERE 2 BCD 200 CHARACTER 10 List of variabies identifiers 2 PILL CHARACTER 36 Unused exists just to make the structure the exact size of one CAIFILES region 2036 bytes DECLARE SC e ee e o ol FEE LEGS EE e e le b e EERE EREEE HES ak e ed oie BE FHKE EKERE REL AK KEKE RES This is the second part of the symbol table It holds the actual type information about each entry whose identifier appears ia C SYM BCD The index of an entry in C_SYM_BCD is also its index in here SINCLUDEd from DCLLIB SYMDDEF fS ok cd e tok tc ck joo be be KEK e e olo oe diee oc kc oe co REE HK ok Sole tok dex EK KK
50. btedly did serve quite a useful pur pose 10 3 THE CAISISTEN DAILY JOBS The CAISYSTEN daily jobs described in Section 7 4 Appen dix A and Appendix B of the Operations Manual need re work ing When CAI was in prime production the level of use of the system warranted high frequency backups and progress reports Current department policy makes it clear that the CAI System will never again support as many users as it once did Therefore the daily jobs will probably no longer be needed Instead a single weekly job to handle file backups and print reports might make better sense 67 10 4 A HELP COMMAND FOR AUTHOR During an author session it would be quite convenient to be able to invoke a help command to provide command syntax information A good first step would be merely to display a Static screen full of suck information and have the user press INT to return to the prior screen format when finished reading Later operands may be added to the command For instance entering HELP LIST would display usage informa tion about the LIST command The information available via HELP could be about author comands DIAL syntax and semantics and even the abnormal termination codes 10 5 WRITING A CAI SYSTEM USER S MANUAL No concise manual exists for an author who wishes to learn to use the system The DIAL architecture and command language description are given in Nudge s dissertation but both are outdated and incoaplete
51. ch screen line Some modules display eatire screens at one tine and the formatting for such a display depends heavily on the screen size Rooting out all such assumptions would require care ful examination of neariy ail of the procedures constituting the CAI system and a tedious modification of many 23 The second strategy for adapting to the new terminals requires more initial work but would be much more satisfy ing in the long run The Hewlett Packard terminals are emi nently more Pophibttcabed than the CC 30s They offer fea tures such as on screen editing programmable function keys Screen paging or scrolling tabs and blinking display and Some can read and write a cassette tape Most importantly all of the advanced features are programmable that is they can be initiated and controlled by special control charac ters received by the terminal from a program The new CHAT System will take advantage of all of these features many of which could add an exciting power to the output capability 0f the CAI system Consider the following excerpt from a hypothetical stu dent session The system displays a screen of new lesson material by issuing the command for the terminal to read and display one of many files on its builtin cassette tape The student presses the RETURN key to signal that he has read the information The system commands the terminal to move the material off screen and lock it into a page of its nenor y The
52. cted almost always mais matched operand types ERROR is set to the appropriate code and CODEGEN returns COMPLER uses ERROR as an index into its array of diagnostics and causes that message to be displayed 2 10 SOURCE This routine is called from AUTHOR to operate on the source code file for the lesson currently loaded It has three entry points GSOURCE ASOURCE and DSOURCE GSOURCE finds the lowest numbered source statement whose number is greater than or equal to the parameter S LNO and returns that statement s text its statement number and its length ASOURCE adds to tie source file the statement whose tert length and number are passed in as parameters AUTHOR tells ASOURCE whether the statement goes at the end of the source file or Somewhere in the Riddle If necessary ASOURCE creates a new block of source code for the added statement DSOURCE deletes the statement whose number is passed in aS a parameter If that statement does not exist in the file DSOURCE returns a failure code 2 11 EXECTOR EXECTOR s prime responsibility is to execute DIAL Delta machine instructions and maintain the activation records Since the machine instructions are stored in regions of the file CAIFILES EXECTOR is also responsible for controlling the paging of instructions and literals That is when it needs to access a new block of instructions it must fetch that page into core via a call to FILEIO EXECTOR is called fro
53. d an impediment Recall that the lessons in the CAI system were no longer useful because they were written before structured programming was generally espoused let alone practiced Naturally the implenenta tion of the system itself predates the creation of those lessons The original code contained dozens of indiscrimi nate and unnecessary branches following the flow of con trol ia many of the code sections was quite difficult The internal comments were sketchy and not generally helpful Little attention was paid to indentation and layout of the Statements The file structures are quite complex and nowhere were they explained in detail A System Progran mer s Manual did exist but was only about half completed Nowhere did there exist an accounting of precisely which elements of the architecture were actually implemented More of a hindrance than any of this however was the fact that the seventeen modules PL I external procedures of the system overlapped in terms of task and effect Most commu nicated with each other through a large number of external variables and only a few were responsible for discrete well defined tasks Modifying such a system is a risk at best at vorst it may spawn a disaster Because each moduie makes assumptions about what changes others have or have not made to the files or data structures a small Change in one may have far reaching and quite unforeseen side effects in any number of others The CA
54. direct access dataset divided logically into blocks or regions Each region is exactly 2036 bytes in length because that was an attribute given it when it waS created In PL I REGIONAL 1 files have the property that each block holds exactly one record Hence there is exactly one key for each region since the file is also KEYED RECORD Keys for PL I files are character strings when CAIFILES was created KEYLEN 9 was specified So each region has a nine character key and the key for each region is simply the character form of the region number For example Region 192 has a key of 192 All input and output to CAIFILES by the CAI System is done by the proce dure FILEIO it is the only routine that knows the file Many routines logically cause I O with that file but only via calls to FILEIO There are 1499 regions on CAIFILES it occupies about 250 tracks of a 3330 disk pack The first ten regions are fixed in purpose they will always contain the same kind of infor nation Pigures 3 through 7 offer descriptions of the information contained on the first ten regions of CAIPILES 23 DCL 1 MAINFILE BASED MAINPTE foo e ok ke ok ook doe olo EKER EEK EK EEE EERE EERE EEK ERE ERE REE EE ERK EE This file is held on Region 1 of CAIFILES it is accessed by on line routines LOGGER to find where to write new log information and SEONOFF to effect recover resume sequence by the on line program
55. e initialized DO NOT EXECUTE THIS PRO GRAM Beference Section 2 2 5 SUMMARY extracts information from file SUMMREC and prints summary statistics at the end of a semester Must be modified each semester to work at all INCLUDEd members SUMMDEF SRECDEF Reference Section 2 4 4 6 SUMMERG merges summary information from two differ ent records into one Used when a student is regis tered for a time under a temporary id and then later under his real one INCLUDEd members SUMMDEF Reference Section 2 3 8 7 SUMMNIT a one shot initialization program for the ISAM file SUMMREC The source is obsolete and this program should serve only as a model should the file ever need to be re created DO NOT EXECUTE THIS PRO G XINCLUDEd members SUMMDEF Reference Section 2 2 65 Chapter 10 FUTUBE WORK This chapter is an informal description of some projects which might be undertaken to streamline or inprove the CAI System The order in which the suggestions appear is not meant to suggest an order of importance There are two major projects that would greatly improve the entire CAISYSTEM a comprehensive conversion to CHATHP and the creation of the CAI On Line File Maintenance CAIOLFM system Both of these tasks are described in A Renovation of the UNC CAL System in Chapter 4 Another project would be to remedy some or all of the known problems and deficiencies of the CAI System These are docume
56. e storage pools This is set from C_SYM_DOPE STR_FREE by AUTHOR It for character variables seems like it ought to also be equivalent to SCB STORAGE S_PTR FREE POINT 1 but I m not sure Ey APERO oleo e o OR oe o ote ak e o k k ok k k k ka EEE k k ak ook Aak RR Ro k k kke k k Source Code Part VERELST EEES EEE EEEE EET EE EEE c ke ook xcd cl E a aa E a E L E E E E E E E E E EEE EE ERE RES 2 BLOCK COUNT FIXED BIN 15 0 Number of CAIFILES blocks 2 MAX LNO 418 FIXED BIN 15 0 2 8 MIN LNO 2 COMPILED 2 SPARET used so far to store source Also the number elements in LCB MAX LNO and LCB BLOCK that are currently in use Maximum line number in each biock Used primarily to find on which block number a particular source Statement resides FIXED BIN 15 0 Lowest line number of the source code changed since the last compile of this lesson Used in AUTHOR BIT 1 CHARACTER 13 2 BLOCK 418 FIXED BIN 15 0 source code resides on 2 CDATE CHARACTER 6 2 CTIME CHARACTER 9 2 SPARE2 CHAR 1 T Figure 15 A Lesson Control 46 x d ud wad aa t Has this lesson been recom piled since the last change Apparently not used The source code directory The n th logical block of CAIFILES block LCB BLOCK n The date t
57. ea A type 2 3 operand means that the operand is a pointer into SCB STORAGE INT if the opcode is appropriate to integers or SCB STORAGE S PTR ERE ERR EEEE E EEE E EE aloe EE E E ES EEE ERE EERE E E EK REE EEE EERE IO E E E E E a 7 3 INT 190 FIXED BIN 15 0 Run time integer values are held here Such a value Bay belong to a DIAL variable of type INTEGER or of type SLIDE In addition the DIAL system integer constants are held here SCB STORAGE INT 1 holds PAUSE SCB STORAGE INT 2 holds 5QZ2 SCB STORAGE INT 3 holds CASE SCB STORAGE INT 4 holds QVAL y SCB STORAGE INT 5 holds AVAL SCB STORAGE INT 6 holds RYAL 3 S_PTR The list of character string vaiue pointers pointing into POOL and POOL2 4 LEN 400 FIXED BIN 15 0 How long is the character string value pointed to by this entry of SCB STORAGE S_PTR 8 ADDR 400 FIXED BIN 15 0 Where in POOLI POOL2 does it start xy FREE POINT FIXED BIN 15 0 Which is the next free xy position in the character storage area POOL1 POOCLIDATA j POOL2 POGL2DATA 2 LESSON CHABACTER 6 Lesson currently being executed held on the SCB instead of just this student s SREC because it may change during the course of the session 2 GLOBALS 18 FIXED BIN 15 0 2 POOLIBLK FIXED BIN 15 0 Next block in student s
58. eased and contain nothing Now further assume that the author begins inserting Statements into another lesson he is working on AUTHOR handles that by calling the SOURCE module Suppose that the block of source code fills up and there is no room for any more source statements on that block SOURCE would then need to create a new block of source code and region 476 just happens to be free at the moment Region 476 could then find itself holding source code when just seconds before it held an LCB This example illustrates the notion of a list of all of the free blocks and some orderly mechanism for claiming blocks for use i e removing them from the free block list and freeing blocks from use i e returning then to the free block list Such a mechanism is embodied in the ALLOTOR routine ALLOTOR maintains the free block list which is held on Regions 4 through 10 of CAIFILES any rou tine which needs a new region for whatever purpose calls ALLOTOR with the request ALLOTOR responds with the number of the block which the caller may use Similarly to free a block a procedure calls ALLOTOR with the number of the block no longer used d1 DCL 1 SCB BASED SCB PTBR ORO ko koe ok koc ok EGE c ook doe oc EK E EE EE S E EE c oc dc deo eoe HEE CREEK ERE EEE EEE AE E S a E E Student Control Block exists for each student in the system It is in effect an activation record for a particular student it x contains cu
59. ed code can take 1 If the code begins with S it represents an OS sys tem completion code Look up the three digit code in the IBM Messages and Codes manual under System Com pletion Codes SCC For instance S80A means that not enough storage was available for a success ful GETMAIN operation 2 I the code lies between 1001 and 1099 inclusive it was generated by the CAI System in response to an error condition it detected but could not fix The routine detecting the error issued a call to the STOP entry point of the EQDQ module which among other things calls the PL I system routine IHESARC IHESARC generates a task return code by adding the given parameter to the retura code normally generated by the system 1000 Therefore CALL STOP 10 yields a return code of 1010 which means that the DIAL compiler s syrbol tabie is full Subtract 1000 from the returned code and look up the error in Table 1 3 The returned code is 2000 This signals a PL I exe cution time error In this case the ERROR condition is raised and the associated ON unit in the main procedure takes controi CAIMAIN calls two PL I builtin functions ONCODE and ONLOC ONCODE returns the code of the error which raised the condition and ONLOC returns the entry point where the condition was raised CAIMAIN displays these two diagnostics and then calls STOP to halt the system 55 17 18 19 20 21 22 23 24 25 26 SNON
60. entitled Use of Branching in this Procedure which lists every Statement label not used just as a loop escape and explains how and when it is used Another modification to the system code was not so modest in nature The modules of the CAI system communicate with each othet through a large aggregation of external varia bles The System was originally built so that all of those variables sere stored in a single large PL I structure and then any procedure which referenced any of those variables was passed the entire structure as a parameter 34 This was done because the load moduie must be reentrant there may be several users at once and each invocation must have its own copy of the external variables The super structure approach worked well but had drawbacks in terms of clarity For instance many of the modules use only two or three of the external variables but had to deciare the entire set taking almost two pages in the listing W James Sneer inger 6 has proposed a more reasonabie solution By dec cb n laring each such variable with the attribute CONTROLLED EXTERNAL and then allocating them all in the main procedure only those variables actually needed by a procedure need be declared there Reentrancy is preserved and Sneeringer argues that the compiled code obtained by this method in fact produces less overhead than that of the structure par ameter approaci Therefore I set out to replace the struc ture in each
61. eter the latter begins the read in the column where the cursor last Was SETROW sets the value of ROW SETCRS positions the cursor on the row of the previous display in the column specified by the parameter SLIDE displays the slide specified by the given param eter A specially encoded parameter may also signal SLIDE to turn the projector on or off DELAY calls the CHAT system delay function to cause a pause of the given number of seconds D DIAG displays the given text usually a system diag nostic message for an author in the bottom two rows of the CRT CAR asks the user to mount a particular slide tray on the slide projector i EDIT implements the EDIT author comgand asking the user to move the cursor to the row on which he would like to enter input EDIT sets ROW to that row 11 Chapter 3 CAI SYSTEM GENERATION Each source module defined ia Chapter 2 shouid be cor piied and linked according to the procedure given in its header paragraph The object modules have usually been stored in the partitioned dataset UNC CS E557C CAI SYSLIB Remember there are two versions of the CAI System The first called CAI is for student use only it does not con tain any of the author facilities The second called CAIAUTH may be used by both students and authors However CAIAUTH uses a large amount of core for modules that a stu dent user will never eaploy That is why the simplified Student version exists
62. g a list of compiler Options to use 8 Use of Branching in this Procedure This is a list of all the relevant statement labels to be found in tne procedure with an explanation of when and how each one is used in branching 9 Other information Some modules may call for special documentation for instance in the main procedure I included a diagram of the overall system call structure and a paragraph explaining the changes made to the archi tecture and documentation of the 1980 system In the DIAL compiler routine the productions of the grammar are catalogued and in the AUTHOR routine there is a list of all of the valid author commands The heading descriptions for internal procedures followed the same conventions with one extension I included a list of all of the externally defined variables used locally by each internal procedure Of course PL I s block structure makes it perfectly legal to use without declaration any variable defined in a containing block but imprudent use of such variables can very easily give rise to side effects and tends to obscure the precise nature of the role of the internal procedure 14 I followed no guide for providing in line comments for the code other than a loose and subjective one First any Major segment of code which accomplished a fairly discrete task warranted a paragraph of commentary If one was lack ing I provided it I decided quite subjectively which were major segment
63. his lesson was last changed The time this lesson was last changed Apparently not used Block n T ez TA Chapter 6 OPERATING INSTRUCTIONS This chapter deals with various operational aspects of the CAI System that may be useful for a CAI System Program mer 6 1 CHATICL CHATJCL is that set of job control language that keeps CHAT and its application programs up and running The CAI System files must be specified in the CHATJCL In particu lar the following two datasets must appear in CHAT s STEPLIB specification Jf DD DISP SHR DSN UNC CS E557C CHATJCL CAI TEST h DD DISP SHR DSN UNC CS E557C CHATJCL CAI LOADLIB Next the three on line file datasets must be identified This is done in the section of the CHATJCL entitled CHAT DD CABDS z AU THREC DD DISP SHB DSN UNC CS E557C CHATJCL CAI AUTHREC STUREC DD DISP SHR DSN UNC CS E557C CHATJCL CAI STUREC C I DD DISP SHR DSN UNC CS E557C CHATJCL CAI CAIFILES Traditionally there has been someone in the Department responsible for maintaining the CHATJCL a CAI System Pro grammer will norsally not have to do it 6 2 MOTH BALLING THE CAI SYSTEN Daring long periods of inactivity in the CAI System it is a good idea to moth ball it This saves valuable on line disk space and reduces the possibility of file damage brought about by an unauthorized person aanipulating the CAI system files To nmoth ball the CAI System 1 Remove
64. his section 2 FILL CHARACTER 1036 Not used makes this structure the exact size of one region of CAIFILES 2036 bytes fos ce she oh he boe le jojo ol oe oe eie io loe e EEEEHKAEKE RK ER EE BER EEE METAR EK ERE ee 7 So for instance the element at the absolute bottom of the stack is FBL SECTION FREE BLOCKS 500 of Section FBL TOP BOS SECTION There are 7 FBL TOP BOS SECTION stack sections not current ly in use and 999 PBL TOP NEXT FREE more regions may be allocated before a stack shift must be done to re fill Sections 0 and 1 Remember allocating blocks empties out the FBL and freeing blocks fills it up f R OR Sk eo eoe iod o ok joke e EEREEE EKA e e eoe ole ke texto ERK ERE EAE EEE HE EEE EEK EEE KE EKER ES Figure 7 PBL SEC Begions 5 10 of CAIFILES 32 The rest of CAIPILES Regions 11 through 1499 may hold one of several kinds of information or nothing at all In particular such a region may hold 1 Ze 3 4 5 a block of DIAL source code see Figure 8 a lesson s compile tize symbol table see Figure 9 a block of a lesson s object code instructions see Figure 10 a block of a lesson s object code literal pages see Figure 11 a block of storage for a lesson s character string variabies see Figure 12 a block of a student s log file see Figure 13 a Student Control Block for a particular student see Figu
65. in are high lighted by appearing in yellow For instance one message is The COMPILE switch is now OFF The ieai is green except for OFF which is yellow If the purpose of the esae is to warn or report failure it appears in yellow For instance You already have a lesson by that name appears in yellow when an author tries to create a lesson with the same name as another When the system halts in case of unrecoverable error the error code appears in red Basically the philosophy is this when the message reports something the user should expect it appears in green when it reports something he should be concerned about it appears in yellow when it announces abnormal termination it appears in red Blue then is left to be the color of the text tnat the user himself enters Of the five new author features implemented three merely replace functions lost when the Llightpen was removed from the systen two are truly new 20 The three replacement functions are CLEAR which allows an author to ask for a blank screen so he may euter a DIAL Statement that was too long to be entered where the cursor was previously positioned EDIT which allows an author to make changes to DIAL text by merely typing in the changes rather than re entering the entire statement and CSW which Gontcols the compile switch the bit which decides whether or not to re compile an author s entire lesson every time the author makes a change to it
66. ing the SYSPUB commands of the University of Waterloo SCRIPT text formatter The file des criptions in Chapter 5 are imbedded directly from the CAI System declaration library UNC C5 E557C CAI DCLLIB the same dataset used by tne procedures of the CAI System to retrieve their declarations from So that dataset must be specified to SCRIPT as tne SYSLIB dataset By using this imbedding scaeme any changes to the file structures will not make the SCRIPT text of this manual obsolete Merely make the changes to the declaration library which would have to be done anyway and re generate this manual In particular the following DCLLIB members are imbedded into this manual they are listed in order of appearance SRECDEF ARECDEF MAINDEF CCBDEF ACBDEF BTOP DEF BSECDEF SCEDEF SYMBDEF SYMDDEF INSTDEF LITDEF PLIDEF PL2DEF LOGRDEF SCBDEF and LCBDEF To generate a copy of this manual submit the following job jiobname JOB account nane T 2 PAGES 100 FORMS 1411 PW password EXEC SCRIPT REGION 300K OPTIONS SEQC 73 CO 25 FNS 1000 lt J Appendix B THE 1975 CAI SYSTEM The system that Mudge and his associates built has remained unchanged since 1975 Even though the newly reno vated 1980 version replaces that system as the production system it is still possible to use the 1975 system The Student only version of the 1975 system is now called OLD CAI The full powered version of the 1975 system i
67. invoked by CHAT on line their load nodules all reside in the PDS 8NC CS E557C CHATJCL CAI LOADLIB along with the load sodules for CAI and CAIAUTH 1 COURSE list the lessons attached to a course and delete lessons from a course XINCLUDEd members PERNDEF CCBDEF LCBDEF Procedures called DISP DELAY E INIT SETROW PASSWRD Reference Section 4 3 3 2 CAIOLFI view the record and current status of a particular student ALNCLUDEd members CHAT SOURCE CCIDCL SRECDEF By calling various entry points of CC30I0 CAIOLFI could no doubt effect its I O the way CAI and CAIAUTH do however by SINCLUDing the CHAT I O declarations CAIOLFI wakes the calls te tke CHAT I O routines directly Reference Chapter 8 61 9 2 OPP LIBB PRODUCTION UTILITIES These utilities are invoked by batch programs although included here are sone subroutines that way be called by the on line programs Their load modules reside on 1 3 Ta UNC CS E557C CAT UTILITY LOAD ACCSLOG prints clears the log of all password accesses XINCLUDBEd members MAINDEF Procedures called INIT EQEXT DQEXT HEADER Reference Section 4 4 3 AUTHREPT prints report giving all personal informa tion lesson names and work times of all authors in the System SINCLUDEd members ARECDEF ACBDEF Procedures called HEADER Reference Section 3 H AUTHAINT utility for adding deleting changing author records in the S
68. ion 0 is then empty once again and ready to be filled up again entry by entry On the other hand when Sections 0 and 1 are both empty because of many allocations the entire stack is shifted up a section at a time ail 500 entries of Section 2 are put into Section 1 and so forth Soho ehe ke oe keel je ke coke tei c e doe eee eoe deese DCL 1 PBL TOP BASED FBL TOP PTR LF ERR EERE od e oe oc KEKE koe doc oe en doc oec coke FBL TOP hoids the top of the FBL stack Sections 0 and 1 of the stack reside here and the entire structure resides on Region 4 of CAIFILES When Section 0 fills up it triggers a stack shift to move all sections down Similarly when Sections 0 and 1 are both eapty it triggers a stack shift to move all sections up one X amp INCLUDEd from DCLLIB BTOPDEF J REEEEEEEE eio dol sod ke obe KEE EO HESEAEAEEE RK ERIE GEER EERE AK EEE EEE ele EERE eek 2 NEXT FREE FIXED BIN 15 0 Which is the next empty element of FBL TOP FREE BLOCKS FBL TOP FBBE BLOCKS NEXT FREE is the absolute top of the stack NEXT FREE varies from 1 to 1000 When it s 1 it s time to shift the whole stack down a section to empty out Section 0 When 1000 both Section 0 and Section 1 are empty and the whole stack must be shif ted up a section to fill up Section 1 2 BOS SECTION FIXED BIN 15 0
69. irect the output to a priat dataset in the CHATUCL as the contents may then be viewed interac tively Such a dataset must have the DCB characteristics of a print file One such file that currently exists in the CHATJCL has the ddname PACPRINT So to send output to the file FACPRINT include the following statement in the main routine of the CAI Systen 51 OPEN FILE SYSPRINT STBEAM OUTPUT PRINT PAGESIZE nn LINESIZE yy TITLE FACPRINT The PAGESIZE and LINESIZE parameters are optional but spe cifying PAGESIZE 20 and LINESIZE 40 should fit the output to a CC 30 screen Now any conventional PL I print state ment e g PUT LIST PUT DATA etc will direct output to this file This method has the additional benefit that when the system ends abnormally diagnostic information is auto matically sent to the print file and without this file spe cification such information would be lost The easiest way to view the contents of your output file is by invoking the CHAT program DISPL DISPL will prompt you for the ddname respond with FACPRINT The first screen full of the file will be displayed by pressing INT you can page through the file If you enter a character string DISPL will scan the file for the next occurrence of that string and dispiay its location When you reach the end of the file however the program ends To look at any part of the file again you must re invoke DISPL n advan tage to this approach
70. is that unlike LOGIT viewing your output file does not destroy it It may be prudent one day to create a print file just for CAI a likely ddname would be CAIPRINT To do that allo cate an on line dataset with print file DCB characteristics Then have the person in charge of the CHATJCL insert a DD card that looks like this CAIPRINT DD DISP SHR DSN dataset name 6 9 GENERATING A HEU VERSION OF THE COMPILER The steps for generating a new version of the compiler arez dn 1 Produce the grammar for the new version using BNF programming and the XPL grammar analyzer See AcKee man Horning and Yortman A Compiler Generator 2 Once the grammar has been thoroughly tested use the BNF program as input to the PL I procedure CONSTRUC TOR This procedure produces punched output which teplaces code sections of the compiler The conpi ler is actually split into three routines COMPLER CODEGEN and TABLES 3 PARSER contains two procedures PARSER and COMPILER Once the code section changes have been made in CON PILER then test data should be run against PARSER Note the listing for the previous run of PARSER contains instructions for converting an existing version of COMPILER into a version to be run against PARSER 4 Once the changes have been verified remove the com piler from PARSER see instructions in the PARSER listing Compile the compiler routines and link them into the SYSLIB object code library 5 Generate
71. ister contents and his Storage for DIAL program integer variables This informa tion is is held in the student s Student Control Block SCB An activation record also contains of the storage necessary for DIAL character strings This is held in two structures known as POOL1 and POOL2 each of which may be thought of as forming half of one very long PL I character string The SCB contains indexing and pointer information about POOLI and POOL2 A student s activation record then consists of one occurrence of each of SCB POOL1 and POOL2 16 Each DIAL lesson has three main parts a source code file an object cede file anda symbol table Each of these parts is stored on a region or regions of the systea s Bain file CAIFILES the lesson s Lesson Control Block LCB contains a directory pointing to each such region Of these three parts ali are used at compile tine whereas only object code pilus of course an SCB is used at lesson exe cution time Now for a more detailed look at the DIAL compilation pro cess The first step in the process is started when AUTHOR receives a LESSON command from an author That causes the initialization of the symbol table the page translation tables the LCB and the source and object code files DIAL statements may then be entered for the new iesson AUTHOR passes each one to COMPLER for compilation and object code generation If COMPLER finds an error it specifies a diagnostic message to A
72. lared to be EXTERNAL they are therefore known to COM PLER These declarations and initializations are held in a module all to themselves for convenience they are produced by the parser generator See Section 6 9 and it is a sin ple matter to store that output in a distinct module There is really no other reason not to internalize them within COMPLEE 2 9 CODEGEN CODEGEN is the semantic action routine of the compiler it is called with a production number just before a reduc tion is Bade by the parser Its basic task is to emit DIAL object code instructions into the structure TEMP There is a section in CODEGEN for each possible reduction in the parse each such section does at least one of the following l Nothing e g in the case of lt IDENTIFIER gt lt lt LEXICAL ID gt 2 Updates the symbol table especially the TYPE infor mation 3 Builds a DIAL object code instruction and puts it into TEMP TEMP INSTNS by a call to its internal procedure EMIT DIAL forward branches are handled with a fixup chain as described under Labels and Branches in Gries 1971 page 280 Run time storage for DIAL character variables is allo cated by CODEGEN when a construction reduces to lt DCL STATE MENT gt unless the variable is taking the default attribute text in which case its storage is allocated as the seman tic action for the lt VAR gt i lt IDENTIFIER gt reduction When an error condition is dete
73. lly written for the system is now embarrassingly outdated It was written in conjabction iti a textbook no longer used and does not reflect the doctrines of structured programming espoused by the books now in vogue Another major reason contributing to the overall problen is the hardware involved in the CHAT systen It is ail showing its age By today s standards the CC 30 terminals are archaic The display is hard on the eyes the screen is quite small and as time passes they are becoming less and less mechanically reliable Spare parts are no longer available In fact each component of each workstation is extremely susceptible to hardware failure Most of the lightpens were long ago disconnected the slide projectors and their controllers are ali moth balled Since the CAI system depends so heavily on CHAT and Since the CAI hardware supported by CHAT seems to be on its last leg the project could very weil have ended here Any work on modifying and rebuilding the CAI system would have been pointless except that under development at the tine of my work waS anew version of CHAT that would allow its application programs to run either on the CC 30 terminals or on the Hewlett Packard 2621 or 2645 terminals recently acquired ay the Department of Computer Science With this new system over the horizon a future for CAI no longer seemed implausible Before that work could be completed however the age of the system once again prove
74. logical structure My restructuring of the code was fairly modest in nature but extremely widespread Like the internal comments this was as much a tool for my own understanding of the system as anything else My first strategy was to delete every GOTO Statement taat I could my tactic was to identify and elimi nate every statement label within each procedure The labels that were branch targets served to point to the branches t enselves The other labels served no useful pur pose and were summarily erased Any mnemonic significance they offered was replaced with a comment Most of the branches that I was able to delete were used to simulate large alternative selection IF THEN ELSE Statements by branching around a section if some condition were not true and falling through it otherwise i replaced those with IF THEN ELSE statements Others were used to build loops I replaced those with loop statements and still others simu lated procedures which I replaced with real procedures After all of the dust has cleared it is evident that the CAI system still suffers from a plethora of GOTO statements Some are used merely to terminate loops and I judged those to be innocuous others are simply too deeply embedded in the logic to be easily replaced For the latter group I adopted another strategy if it can t be eliminated then it must be explained Therefore as explained above the documentation for each module includes a paragraph
75. ly fornmat ted ids are given 2 two unknown ids are given or 3 an attenpt to enqueue a required resource fails If the sign on is successful and the user is a student then either a resume or a recover sequence takes place according to the RECOVNEEDED bit in the student s SREC structure read from file STUREC A resume is what hap pens when the student s last session ended normally The system restores his run time environment by reading it into core from his resume area on disk where it was stored when he signed off from his last session This time there fore he will start in a lesson about where he left off last time A recover is what happens when the student s last session ended abnormally e g the system crashed before sign off For more about resuming recovering and the file I O involved see the declarations for MAINFILE SCB and SREC also the in line comments of SNONOFF attempt to give a good idea of the protocol involved If the user is an author SNONOFF calis SYS_S to make sure that this system was generated with complete author facilities If not the sign on fails The record of the student or author SREC or AREC is updated written and freed The structures SREC and ABEC and therefore the ISAM files STUREC and AUTHREC will not be used again until signoff SNONOFF then returns to CAI MAIN informing it whether the user is a student or an author If the function is to sign off a user the
76. m CAIMAIN if a student has signed on In that case it uses the current run time environment for that student which was set up by SNONOFF during the resume recover sequence to discern the statement in the lesson in the course to begin execution with When the les Son is finished EXECTOR asks the student whether he wishes to continue to the next one and perforas according to the given response EXECTOR is called from AUTHOR if the user is an author In that case there is no run time environaent for the stu dent EXECTOR creates a dummy activation record which disappears when execution is complete EXECTOR knows who is calling it by checking the value of the external variable SNONCODE 2 12 PATPROC PATPROC contains EXECTOR s external subroutine for imple menting the DIAL system pattern matching function Basi cally the student s response is passed in and checked for the occurrence of a given character string pattern also a parameter PATPROC returns a bit value indicating match or no nmatch The pattern may contain cent sign don t care symbols For an explanation of the architecture of the DIAL system pattern Batching function see Section 4 7 of Hudge s dis settation 2 13 LOGGER This module is called by EXECTOR while in student node its purpose is to record every typed response issued by a student to a question and to record the execution of every Statement of a lesson This is a statistical and analytic t
77. meter PASSWRD returns a 1 otherwise it returns a 0 SINCLUDEd members PERMDEF MAINDEF ACBDEF 63 16 17 18 19 20 21 Procedures called FILEIO 4D DIAG DELAY DISP RD2 T RMV_DIAG LOGIT a CHAT routine provided at load module generation time as it is in the on line systems Reference Section 7 3 4 PRINT prints an author s directory and the object code literals and syabol table for a specified les son This is a substitute for an envisioned on line PRINT command SINCLUDEd members PERMDEF LCBDEF SCEDEF SYMBDEF SYNDDEF INSTDEF LITDEF ARECDEF EQDQEXT Procedures called ACBPROC GSOURCE FILEIO INIT EQID DQID Reference Section 7 1 SAYINIT clears and initializes the LOGSAVE tape Reference Section 7 3 3 STUDUMP prints part of the specified students cur rent SREC file information INCLUDEd members SRECDEF Procedures called HEADER Reference Section 2 4 3 STUMAINT inserts deletes changes student records in the System X INCLUDEd members SRECDEF SUHMDEP EQDQEXT Procedures called INIT F EQEXT DQEXT EQID DQID HEADER LOCATE Reference Section 2 3 STUREPT prints a progress report for a given stu dent Included are the amount of time spent by the Student number of recovers and resumes and course and lesson currently being viewed by the student X amp INCLUDEd members SRECDEF EQDQEXT Procedures called HE
78. n SHONOFF recalls whether the user is a student or an author If an author his record is updated with data from this session and written back onto AUTHREC If a student his SCB is written onto the SCB PART of his SREC for use in his next session s resume sequence he will begin work next time at a piace near where he left off this time His SREC is then updated and re written onto file STUREC 2 3 PULLCAI The module FULLCAI consists solely of the procedure SYS_SN All this procedure does is return a bit value of false to be tested by SNONOFF When an author signs on to the system SNONOFF calls the procedure SYS SW to see whether this is the version of the System that supports author facilities When that version of the system is gen erated this module is included When the Student only ver sion of the system is generated the STUONLY module is included instead its version of SYS SW returns a true bit value and informs SNONOFF that oniy students may use that system See Section 3 1 of this manual for further information 2 4 STUONLY This module like FULLCAI consists only of a version of the procedure SYS_SW that returns a true bit value informing SNONOFF that the system that has been generated does not include the author facilities This allows SNONOFF to prevent an author from signing on to a student only ver sion of the system See Section 3 2 of this manual for further information 2 5 AUTHOR AUTHOR i
79. ndentation become easier This policy is certainly not without precedent TSO for example employs it One may argue that I made this decision for the wrong reason ease of implementation but I submit that the final result is in fact a better architecture In fact I would hope that my modifying work has produced exactly that a better architecture throughout I am confi dent that it has produced a better implementation in terms of clarity efficiency and ease of future change The CAI System is still not the invaluable aid hoped for by any of its creators it is however a viable tool which I have tried to make easier to use 22 Chapter 4 SUGGESTIONS FOR FUTURE DEVELOPMENT The event that may breathe new life into the CAI system will also precipitate the next major requirement for change When CHAT is able to run on Hewlett Packard terminals a major overhaul of the CAI system will be in order Two strategies are possible The first is to adapt the system to the new terminals by applying local fixes Even though terminal input and output are technically done by only one procedure in the systen almost a dozen procedures make the assumption that the schodd Size of the terminal is that of a CC 30 which is quite different from that of the Hevlett Packards The most common example of this is creating a muiti line display mes Sage by inserting the appropriate number of blanks rather than a new line command at the end of ea
80. ned new version of the CAI system Finally the deletion of the lightpen facility has served to reduce the amount of run time memory required by the system and to streamline tne system in the sense that input can now only be done via the terminal keyboard This I believe is inportant froh human factors standpoint Neither the student nor the author need worry about using the lightpen which seems to me to be a rather unnatural input mechanisn It was the deletion of the lightpen that allowed my system to ase Slightly fewer PL I statements than its predecessor while actually doing more work Tae system diagnostic messages were modified in two ways First I attempted to make them more informative and more congenial For instance the sign on greeting UNC CAI SYS TEM displayed in bland blue was replaced with Welcome to the UNC CAI System shown in a more congenial green i added some messages For instance some commands in the system ask an author whether he really wants something done if he fails to confirm it the command is nullified The old system responds merely by waiting for another command My version acknowledges the cancellation and displays in green Command canceled Finally I paid special atten tion the color of tae displayed message Previously most diagnostics appeared in blue I adopted a more varied Scheme If the purpose of the message is to confirm or inform it appears in green Special words with
81. ng the Student Only Version CAIl a a 14 Notes Concerning System Generation e 14 Generating a System to Run under CHATHP 15 THE TRANSLATION AND EXECUTION OF DIAL CODE a 16 5 CAI SYSTEM DISK INPUT OUTPUT a gt gt gt gt 18 STUREC The Student Record File gt 18 AUTHREC The Author Record File a s e a 21 CAIFILES The Heart of the CAI System gt 23 6 OPERATING INSTRUCTIONS 2 2 2 a T CHATJCL 2 e had gt 2 LJ 47 Moth Balling the CAI System gt a 47 Author Command Facilities e Addenda to the DIAL Specifications Proctor Override Facility OPEXEC 2 LJ Ld gt Using the PL I Optimizing Compiler i ba Debugging Aids gt 2 ew a s Generating a New Version of the Compiler E gt e Ta ABNORMAL TERMINATION CODES a a gt gt gt 8 PROTECTION OF CAISYSTEM DATASETS o a gt gt Using tne OS ENQ and DEQ Facilities Dataset Backups and Restorations gt 9 THE CAISYSTEM UTILITY PROGRAMS gt a On Line Production Utilities e a a Off Line Production Utilities a gt Non Production Off Line Utilities 10 FUTURE WORK e a Removing AUTHREC from the On Line System Bejuvenating
82. nt displays and another commana that would allow that text to be written onto a cassette tape and referred to symbolically there after much like the SLIDE data type currently implemented in DIAL Then there might be a SHOW TAPE command and a SHOW HIGHLIGHTED TAPE command The possibilities are pro fuse 25 A second major improvement to the CAI system would be the implementation of an on line file maintenance subsystem This was envisioned By the original team of CAI system pro grammers and still seems a good idea There are three major files used by the CAI system One contains informa tion about all authors known to the system another about all students known to the system and the third contains everything else for example the source and object code for all the lessons the list of lessons constituting each course the status of each student currently taking a course and so forth To add or delete or change records in these files single purpose batch programs must be sub mitted A more elegant solution would be to invoke an on line CHAT program which wouid be able accomplish any of the tasks now handled by the batch programs The list would include adding an author or a student to the system delet ing an author or a student from the system deleting all Students enrolled in a particular course from the system reporting on a pirkicular student s progress displaying a directory of all students or authors currently in
83. nted in a hand written list kept in the back of the CAI Operations Manual This list should be kept up to date as it serves as a valuable and convenient way to keep up with system probleas 10 1 RESOVING AUTHREC FROM THE ON LINE SYSTEA The keyed ISAM file CHATJCL CAI AUTHREC could be removed from the on line system It is composed of instances of the structure AREC containing for each author his name and address his id when he entered the CAISYSTEM and how many hours and sessions he has had at a terminal The on line system sets the last two items and SNONOFF accesses his id as the key to the file SNONOFF does this at sign on time reading the author s AREC into core Since all the id s are also stored in the ACB SNONOFF need not ever use AUTHREC The off line program AUTMAINT puts the information about a new author into AUTHREC by creating a new instance of AREC It also nust update the ACB Now all that SNONOFF would have to do to see whether it had an author signed on would be to make a single call to ACBPROC asking it to verify an author id AUTHREC need not ever appear in the on line sys tem and could in fact be taken out of the CHATJCL and put on an off line volume somewhere What this would mean is that the on line system would no longer be able to record the number of hours sessions but no one uses that informa tion anyway the CAI system is no longer experimental 66 Now if CAIOLFM were ever built or CAIOL
84. ogfiles on MAINFILE During processing of STORECH OP 34 instruction COMPACTIFY was called but did not free enough space for the next string operation During execution of the ON ERROR unit the ONCODE was not found in the table of codes ONCODES 0 99 Compiler Debug Stop 1 in PLISEG production No room left in STORAGE INT 56 27 28 29 30 31 32 33 34 35 36 37 38 39 40 54 54 EXECTOR EXECTOR EXECTOR EXECTOR EXECTOR EXECTOR EXECTOR AUTHOR EXEC TOR AUTHOR SOURCE EQDQ EQDQ FILEIO FILEIO FILEIO FILEIO FILEIO FILEIO ALLOTOR AUTHOR ALLOTOR FILEIO SNONOPF During setup for execution in the case that IC lt 0 no next lesson found Addressing error Page decoded fros IC is greater than I PAGES CT Addressing error Page decoded fron Ic is less than 1 Addressing error in student only aode No ENDLESSON instruction at end of lesson system tries to execute beyond the lesson s last instruction Addressing error IC was about to retrieve an instruction in the last page of the lesson but beyond INSTNS NEXT FREE This is a DIAL system software error In FETCH21 the page decoded is greater than L PAGES CT In FETCH21 the pages decoded is less than 1 During a PURGE lesson name was echoed correctly but ACBPROC failed to find the lesson on the ACB When setting up for a student beginning a course IC 0 no lessons were found on the CCB In Stage
85. on to be taken when the student s response falls through all of the associated MATCH statements There are more complex forns of both the MATCH and UNREC statements offering more flexible actions but the fact that both rely on explicit branching to do what could be accomplished without it seems to me to be unwieldy AS a result DIAL programs must rely heavily on branching and this offers little chance for structured author programming which in turn makes course writing all the more time consum ing and awkward For instance consider how the first example above would be formulated with oniy the incomplete DIAL available READ MATCH expected answer RIGHT SHOW Wrong answer try again GOTO DONE RIGHT SHOW Your answer is correct DONE end of if then else simulation Or for the third example READ MATCH expected answer OUT OF LOOP SHOW Wrong answer try again GOTO READ OUT OF LOOP end of do while simulation The case statement Simulated in the second example above would offer an even more dramatic display of labels and branching As for the fourth example which branches condi tionally after testing tho value of a counter variable it is not clear to me that in the limited version of DIAL that would be possible at all It is for this reason that I believe CAI has fallen dor mant no one has been villing to compose new lesson material for the systen and as a result the PL C course origina
86. ool designed to let the author see the responses evoked by his questions Each student s log record consists of a chain of the structures LOGRECORD MAINFILE keeps track of all of the Chains Each structure is stored on a region of CAIFILES A student s LOGRECORD stays allocated throughout the execu tioa of a lesson and is written to disk when the execution is terminated From time to time all of the log records are removed from CAIPILES and written onto tape by the off line utility program CAILOG MAINFILE is cleared of all of the references The tape may then be analyzed and summar ized by an off line program which does not yet exist 2 14 PELELO FILEIO is the generalized file input output procedure which the system uses to communicate with its main file CAIFILES The functions which FILEIO can perform include reading writing opening closing and rewriting the file Moreover if a read is to take place on Regions 1 through 4 of the file which are serially reusable resources of the System FILEIO makes the necessary calls to the enqueuing and dequeuing procedure t EQbBQ For further inforRation about the CAIFILES file see Sec tion 5 3 of this manual For information about the parts of that file which are serially reusable resources see Section 8 1 2 19 ALLOTOR ALLOTOB is a utility routine called by other procedures of the CAI System which need to use blocks of storage regions on the main system file CAIF
87. our answer is correct 3 Or IF answer wrong answer 1 THEN SHOH hint 1 ELSE IP answer wrong answer 2 THEN SHOW hint 2 ELSE IF answer wrong answer 3 THEN SHOW hint 3 ELSE SHOW big hint Or Read answer DO WHILE answer a expected answer SHOW Wrong answer try again Read answer END Or finally I 0 Read answer DO WHILE I lt N amp answer expected answer SHOW Not right yet try again r3 1rp 14 Read answer END DIAL s control structure for answer analysis is the MATCH Statement Syntactically it is of the form MATCH expected answer iabel and it the student response is expected answer then a branch takes Implicit in the first HATCH statement Statement is the command to read an input equivalent to place to label following a SHOW line from the dis play screen Similarly there is the UNREC statement UNREC label1 label2 label3 where the i th unrecognized response to the most recently executed SHOW statement will cause a branch to the i th label in the UNREC label iist Ah unrecognized response is one that has not been specified in the MATCH statement s following the controlling SHOW statement The UNREC state ment corresponds to the OTHERWISE statement of the PL I SELECT construction It relieves an author from having to test via MATCH statements for every possible student input Rather it allows the author to specify an acti
88. p a student s entire Delta machine run time activation record When there is not enough room left on POOLT POCL2 to store another string EXECTOR s internal routine COMPACTIFY operates to compress the strings and the pointers in SCB STORAGE S PTR Between sessions for a particular student my POOLI and POOL2 data parts as well as SCB are copied into the student s SREC on file STUREC The reason that all three are the size of CAIFILES regions is the resume recover protocol of SNONOFF When a student sigas on his activation record is stored in CAIFILES When he signs off it is saved in SREC and deleted from CAIFILES That way if the session ends abnormally before the save onto STUREC the system will have saved a reasonably up to date activation record for him Remember only the DATA parts are stored in SREC The whole structures POOL1 and POOL2 are used either in core or in a student s RESUME and RECOVER areas on CAIFILES INCLUDED fron DCLLIB PLIDEF foo ek obe ood ok coke tc kc ke ic d olo OR IO ESE EE EEE EEE EE E E E E 2 POOLIDATA CHARACTER 2032 2 POOL2BLK FIXED BIN 15 0 Points to the CAIFILES block 2 C POOL2BLK amp PIXED BIN 15 0 Points to the CAIFILES block DECLARE holding this student s RESUME area POOL2 structure holding this student s xy
89. procedure with only those variables actually used and I believe that the gains in clarity are well worth the effort Even though the modules still communicate through external variabies each module at least contains a list explicitly defining the only variables it may change In addition 1 discovered that half of the fifty external variables did not in fact need to be known to more than one external procedure and they were quickly demoted to local variables The new System Programmer s Manual is included as an appendix to this document The sections that I supplied are listed in an appendix to the manual It should be noted that much of the information added to the manual cane directly from the internal documentation of the system For instance the module descriptions are from each procedures Function paragraph in the header comment Although time has not permitted removing all of the defi ciencies pointed out in Chapter 2 the architectural modifi 18 cations I have made include extraction of the lightpen from the system color coding and re wording of the system mes sages to the user and the implementation of five new author command features The ligatpen facility was taken from the system for three reasons The first is that for all practical purposes there are none left nearly all are out of service The second reason is that the Hewlett Packard terminals do not feature lightpens Reade neither will the envisio
90. re 14 a particular lesson s Lesson Control Block see Fig ure 15 33 DCL 1 SOURCE BASED SRC PTR f Shoe ce e eoe oko ole oe BEE e ooo dole ok ete EAE ERE EE EASE REESE EERE EEE EE SOURCE is what a CAIFILES source code block looks like The x LCB for a lesson contains a list of all the blocks for that lesson which contain its source Each one looks like this The actual source is held in SOUBCE DATA The index of that space is contained in SOURCE DIR 2 Each block of source code can contain forty statements or 1792 bytes whichever is less amp INCLUDEd from DCLLIB SCEDEF fO OR ook did EEEE EEEE EEEE ETES EE EEEE E EEEE EEEE FEE AE AER eie EEE ES E E E E E EE A 2 DIR 2 40 The directory into SOURCE DAT The I th source state ment held in this block has a statement number of SOUBCE DLNO I is SOUBCE DLEN I bytes long and is in SUBSTR SOURCE DATA SOURCE DLOC I SOURCE DLEN I 3 DLNO FIXED BIN 15 0 3 DLEN FIXED BIN 15 0 3 DLOC FIXED BIN 15 0 2 FREE LINE FIXED BIN 15 0 The next free element of SOURCE DIR 2 1 e there are FREE LINE 1 statements currently heid on this block i e in this structure 2 FBEE POINT FIXED BIN 15 0 The next free location in the pool of source code SOURCE DATA xy 2 DATA CHARACTER 1792 The pool of characters which make up the source statements held on this
91. rest of CAISYSTEM i e the off line programs are described herein but only briefly Chapter 2 THE EXTERNAL PROCEDURES CONSTITUTING THE CAI SYSTEH There are seventeen distinct external procedures which when linked together form the on line programs CAI or CAIAUTH This chapter contains a description of each one Note that the text comes directly from the header paragraphs for each module Information about the logic of each proce dure may be found by consulting the comments in the source code listing of that procedure Tae overaii function vill be emphasized herein not the actual implementation strategy employed to achieve that function 2 1 CAIMAIN CAIMAIN is the main procedure of the on line CAI System It contains the ON ERROR on unit which allows the system to display fatal crror diagnostics before it dies it aiso calls SNONOFF the sign on off routine to see shether an author or a student is the user On the basis of that call CAIMAIN either calls AUTHOR or EXECTOR Finally another call to SNONOFF occurs for sign off and the task termi nates 2 2 SNONOFF This routine performs user Sign on and sign off fuac tions depending on the value of a given bit parameter If the function is to sign ON a user SNONOFF reads the user id from the screen and accesses the AUTHREC and STUREC files to see if it belongs to a student or an author res pectively or neither A sign on attempt may fail if 1 two incorrecti
92. rrent Delta machine status register contents and state switches and run time storage for DIAL lesson variables integers for INTEGER and SLIDE types and pointers into POOL and POOL2 for CHARACTER types n SCB also points to its student s RESUME and RECOVER file areas EXECTOR s internal procedure INIT SCB performs all initialization of the SCB except for GLOBALS during its begianing of new lesson sequence The procedure EXECTOR is the primary user manipulator of SCB Between sessions a student s SCB is stored in the SBREC SCB PART for that student Because of the re entrancy of the system each student gust and does have his own SCB and thus has his very own private Delta machine However it is easier not to think about many students and many SCBs and many Delta machines all operating at once In stead nothing is lost by pretending there is only one of each the re entrancy takes care of itself RINCLUDEd from DCLLIB SCBDEF Seco kc kool kc ok RR oleo ke tool oe EEE IE EEA REESE EE ERE EEE RE EEE RRR KE FOR BE k BABB ce ce ROGER c e C e bc k e e RO SRO e c RR IO k k Current register contents of this student s Delta machine S00 oo ek ook koe kc IA cj e ole jo doe ESEE ESE ak ia S to EET EEEE EEE E 2 IC FIXED BIN 15 0 The instruction counter x IC tells what statement in the current lesson
93. rts of the object code file need not be discarded Improvement in run time performance might be attained by optimizing the object code at ATTACH time In particular useless NOP instructions could be deleted and object code pages could be compressed 10 7 MODIFYING DIAL Mudge Chapter 9 offers some view about extending the author language and the reader is referred there One extension which seems especially useful and promising would be the PARSE system matching function which would take a gtammatical specification of a construct and see whether a student s response parsed correctly under that construct Such a function it seems would greatly simplify answer analysis in programming language lessons but its use would certainly not be limited to such an application A more immediate task should be the creation of a new DIAL grammar whether for an extended or completely new author language or for the one which is now in place The grammar is needlessly complex there are many unnecessary productions of the form nonterminal terminal Further the grammar biurs the distinction between arith metic and string expressions there is even one production of the form string expr gt lt arith expr gt and necessitates Buch run time type checking by the EXECTOR module Nany constructions which are syntactically legal are semantically disallowed forcing the code generator and the executor to do more work than would otherwi
94. s and waich were not Second any other statement or segment whose purpose was not clearly explained and that seemed important enough to try to under stand received an explanatory comment Again the deci sions here were subjective I tried not to be terse Often I was forced to understand a group of statements in order to effect my architectural modifications and then it was a sinple matter to record what I had learned about a certain section By the same token those parts of the sys tem that clearly did not apply to my work may remain some what under documented While my nodified System actually comprises toughly tuo percent fewer executable PL I statements than its predeces soc the source listings occupy some fifty more pages an increase of about eighteen percent I attribute most of that to new internal documentation Naturally that does not speak to the quality of the added information but should at least offer evidence of my good intentions An adjunct to the internal documentation was the work I did to to improve the visual quality of the code The rules applied were quite simple They included uniformly indenting the bodies of loops and compound statements including any contained comments describing parts therein aligning each END with its associated DO and indenting each code section beneath the comment describing it The result ing physical structure of the code is meant to aid the understanding of its
95. s are loaded when AUTHOR receives a LOAD command for later use by COMPLER 2 I PAGES CT FIXED BIN 15 0 How many instructions pages blocks of object code in structions have been used so far also how many elements of LCB I PAGES are currentiy filled 2 L PAGES CT FIXED BIN 15 0 How many pages blocks of character string literals have been used so far Also how many elements of LCB LITAREAS are currently filled 2 I PAGES 64 This lesson s instructions pages directory 3 BLK FIXED BIN 15 0 The page translation table for th instructions pages The table is in logical page order i e the n th iogical page of instructions is held on CAIFILES block number LCB I PAGES n BLKtE 3 LARGEST LN FIXED BIN 15 0 The highest source code line number in the page This is used to translate the M into instruction counter IC form when AUTHOR receives a XEQ M N command or EXECTOR receives a PROCTOR N command 2 LITABEAS 32 FIXED BIN 15 0 The page translation table for the literal areas The n th logical literal page is on CAIFILES block number LCB LITAREAS n This is built by COMPLER it is used read only by EX CTOR 5 ui d i d A 2 S PTR COUNT FIXED BIN 15 0 The number of elements now in SCB STORAGE S PTR which is the list of pointers into POOLI and POOL2 the run tim
96. s now Called OLDCAIA It should be pointed out that the 1975 system and the 1980 system both operate on precisely the Sage datasets In terms of file handling and lesson manipulation the Systems are almost completely compatible That is a lesson created under one system may be loaded listed attached changed purged or renamed successfully using the other system The resequencing command however is an excep tion That command is not supported in the 1975 system and expects lessons to have four digit line numbers in the 1980 system In terms of DIAL programming the two systems are also nearly compatible That is a lesson created using one sys tem may be re compiled and or executed using the other There are two exceptions The 1975 system does not support integer addition The 1980 system does not support lightpen facilities So any lesson containing either of those two features is bound to the system under which it was created The source code for the 1975 system is on the partitioned dataset UNC CS E557C CAI75 SOURCE it is also stored on a tape The 1975 system s object modules and DCLLIB dataset are also on tape See the Operations Manual for details s UO 1 3e y 5 REFERENCES Bassman Mitchell J UNC CAI System Operations Manual University of North Carolina at Chapel Hill 1975 Gries David Compiler Construction for Digital Computers Wiley New York 1971 McKeeman W M Horning J J and
97. s room for 184 ACB NEXT FREE 1 more lessons in the ACB There is room for 40 COUNT more authors in the system J RPRRERERE RE eoe EEE KEE RE EE EEERE EREEERER EEK EEE ERE RERERE ES PEE KE E 28 Figure 5 The Author Control Block Region 3 of CAIFILES 29 ffo Re olo ERE EER EE ESE EEE EREEE EERE EE EEE olore EEK EE ERE EEE EEE EEE kkk ek The Pree Block List FBL is a list of all of the CAIPILES regions that are not currently in use Regions 1 thru 10 are always in use containing MAINFILE the CCB the ACB and the FBL The other regions gay for example contain sections of DIAL source code or object code an LCB an SCB a LOGFILE etc The FBL is a stack composed of eight sections Each section can list 500 entries Sections 0 and 1 are both on Region 4 of CAIFILES although they are defined to be two sections they in fact act one double large section of the stack The rest of the stack Sections 2 thru 7 are on Regions 5 thru 10 respectively with one section per region The top of the stack i e where the pushes pops take place is Section 0 or 1 depending on how full the 1000 element free block list in FBL TOP is They are the only sections of the stack that fills up or empties out one element at a time When Section 0 fills up the whole stack is shifted down A SECTION 500 ENTRIES AT A TIME Sect
98. s the prime interface between an author and the CAI System It is called as soon as CAIMAIN learns from SNONOFF that it is an author not a student who has signed on AUTHOR converses with its user via the command language and line numbering mechanism It is the facility that allows an author to enter DIAL statements and have them com piled by invoking the syntax directed compiler for each statement received This procedure not COMPLER builds the object code and source code files for a lesson COMPLER compiles one state ment at a time it merely returns in the structure TEMP the object code and literals for that one statement AUTHOR takes the contents of TEMP and adds them to the instruction and literal files for the lesson being worked on AUTHOR is forever updating the lesson s Lesson Control Block LCB to keep track of for example the page translation tables and CAIFILES region allocation Also AUTHOR sets up and controls calls to EXECTOR in response to an author s request to view the execution of one of his lessons 2 6 ACBPROC This procedure is called by AUTHOR to perform processing on the Author Control Block ACB held on Region 3 of CAI FILES Given a lesson nane it performs according to the requested function parameter Its functions include search ing the ACB directory to find out where the given lesson s Lesson Control Block LCB is stored removing the given lesson from the ACB returning its LCB location
99. se be necessary Another example is the peculiar way in which the grammar treats IF THEN ELSE and DO WHILE statenents The ELSE part is considered to be a statement in itseif Thus it is syn tactically legal for an ELSE clause to appear by itself anywhere in a DIAL program Similarly the ENDDO statement may appear anywhere and the syntax does not care whether or not there is a corresponding DO WHILE That currently causes no problems since neither feature of the language is actually implemented However a new grammar would surely be in order before their implementation is attempted Finally the implementation of those two statements Should be attempted They would provide much needed relief from the GOTO mania imposed by the rest of the DIAL lan guagee Moreover the IF THEN IF THEN ELSE construction Should include compound statement do group capabilities 69 Appendix A NOTES ABOUT THE MANUAL A 1 HISTORY OF THIS MANUAL Tne original CAI System Programmer s Manual was a hand typed documented prepared by J Craig Mudge in 1973 It was modified later that year by O Jack Barrier and again by Mitchell J Bassman in 1975 In 1980 it was text formatted and enhanced by Paul C Clements to complement the newly renovated CAI System The 1975 manual exists in the 1980 version as the follow ing parts Chapters 4 7 and 8 Sections 3 1 3 2 6 5 6 6 and 6 9 2 GENERATING THIS MANUAL Tnis manual was written us
100. system displays a question and the student responds The system instructs the terminal to record the response on its other cassette tape for later analysis On line response analysis takes place as usual and the CAI system discovers that the student s answer is wrong It orders the terminal to page the lesson material back onto 24 the screen this time however key words and lines of the Screen are highlighted with an inverse video or a flashing displajy The student is asked the question again and this time he responds correctly The system displays the congra tulatory message rings the terminal s bell and goes on to present the next topic Of course to realize such a situation would take an inordinate amount of work But such powerful capabilities present a Droad range of possible enhancements to the CAI system It seems to me that a reasonable first step would be to build a CAI system so that only one module truly knew of the terminal characteristics It would be responsible for fitting given text strings to the available screen size Perhaps the calling procedures would adopt command paran eters similar to what might be found in an elementary text formatter center underscore newline table etc After that new DIAL commands may be created For instance one might visualize a feature that would allow an author to define a screen full of text Specifying which words or lines should be highlighted on subseque
101. t Sign on time copied from there at sign off time y 2 POOL2_PART CHAR 2036 Copied into POOL2 POOL2DATA at sign on time copied from there at sign off tine xy Figure 1 odel of a STUREC Record SREC 20 5 2 AUTHREC THE AUTHOR RECORD FILE AUTHREC is an ISAN dataset containing author records For a description of the creation and maintenance of this file consult Chapter 3 of the CAI Operations Manual AUTHREC is declared thus DECLARE AUTHREC FILE RECORD KEYED UPDATE DIRECT ENVIRONS ENT INDEXED Input output is by the usual PL I statements READ FILE AUTHREC INTO structure name KEY AUTH ID WRITE FILE AUTHREC FROM structure namej KEYFROM AUTH ID The records in file AUTHREC are instances of the PL I structure AREC AUTHREC contains all pertinent author per sonal data and CAI status See Figure 2 for a complete des cription of the record format of the AUTHREC file 21 DECLARE 1 AREC CONTROLLED J S08 X ke pee e te e e nee oe ke ng e eic a ol oe e ke c X e c e o bo doo oo ok eoo Each instance of this structure is a record on the keyed ISAM file CAI AUTHREC CHATJCL The file contains personnel and work information about each author known to the CAISYSTEM The file is used by the on line module SNONOFF to compare the given sign on id to know author id s It is also used by off line maintenance routines such as AUTHREPT and AUTHAINT It is
102. t has spend on the course he s now enrolled in Excludes time from abnornally ended sessions 2 SESSIONS 3 WRECOVERS FIXED BIN 15 0 How many recovers have been done fot this student i e how many sessious have ended abnormally so far 3 NRESUMES FIXED BIN 15 0 How many resume sequences have taken place for this student i e how many sessions have ended normally so far x 2 COURSE CHABACTER 6 What CAI course is this student taking 2 RECOVNEEDED BIT 1 ON means last session ended abnormally and the student s activation record will have to be obtained from the RECOVER area at sign on time Can also mean that this student has a i session in progress right now 2 COURSE END BIiT 1 Has student finished the course SOOO ook A oc EK ERE EE ERE EE qoc ee doe joe E AE EK boleto k okk k k E kk Ek PART II The copy of the student s activation record saved in his SREC on the ISAM file STUREC between sessions The activation record is composed of three parts the Student Control Block SCB POOL and POOL2 VEEE EES EEE EE EEEE EEEE EEEE EEE EK AE dote doloe ok EEE EKER EEE EERE ERE RE EEE EEK 2 SCB PART LIKE SCB Copied into the in core SCB at Sign on time SCB copied into here at sign off time 2 POOLI PART CHAR 2032 Copied into POOLI POOLIDATA a
103. the CAI Operations Manual The CAISYSTEM Daily Jobs gt A HELP Command for AUTHOR gt Writing a CAI System User s Manual Improving Lesson Re Compile Time Modifying DIAL aa gt gt gt 6 4 8 s e a a g d Appendix A NOTES ABOUT THE MANUAL saa e a eee History of this Manual Generating this Manual oe a a gt 8 8 i L L B THE 1975 CAL SYSTEM a v a2 o 2a gt REFERENCES 3 w 9 gt o 9 a iv s 8 e 8 e a 5 d t e 5 5 o tt 285 d 49 49 50 50 51 52 59 60 Chapter 1 OVERVIEW OP THE CAI SYSTEM The CAI System can be thougat of as consisting of two constituent sets of PL I procedures One set makes up the on line system that is that system which appears to the user sitting down at a CC 30 terminal and signing on toa CAI program under CHAT The other routines are off line executed by batch jobs they perform file maintenance tasks and the like There are three on line systems of CAI They are invoked by signing on to CHAT and entering the appropriate program name The first is called COURSE it is an on line program for displaying and removing lessons from a CAI course This is important because a course cannot be deleted from the CAI System until all of its lessons have been removed The second on line program is called CAIOLFI for CAI On Line File Inquiry
104. the module description in Section 2 16 for a descrip tion of each 59 Resource 6 STUDENT any student signed on Resource 7 AUTHOR any author signed on 3 Finally the third group is used to prevent tuo users from signing on to the on line system with the Same identification number When a ser signs on whether student or author his identification number is enqueued and remains so until he signs off Resource 8 ID All enqueuing and dequeuing is done by the sodule EQDQ however only certain other modules call EQDQ to request such enqueuing dequeuing The module FILEIO controis alilo cation of the CAIFILES shared blocks A resource is enqueued when a read to that block of the file is requested The dequeue request is issued when a REWRITE to that file is received The enqueue request is for exciusive control and with the condition that the task wait until the resource is available The CAISYSTEM resource is controlled by the module CAI MAIN The STUDENT AUTHOR and ID are handled by the SNON OFF module The enqueue request is for shared control with the condition that the task not wait if control is not immediately available If that is the case SNONOFF dis piays a failure message to the user returns to the main procedure and the system terminates Off line utility routines requesting any of these resources do so with exclusive control specified This pro vides a lockout if the resource is already in use
105. this this student s LOGRECORD DATA 2 FREE POINT FIXED BIN 15 0 Next free byte in LOGRECORD DATA USED WHEN BUILDING LOGRECORD 2 DATA CHAR 2014 FORMAT 1 DIAL lesson line FIXED BIN 15 0 2 Length of response FIXED BIN 15 0 0 means no response was given just a plain interrupt vas received 1 800 means the actual response length 801 means no response at all was given or expected used in the open close operations 3 What time response was made CHAR 4 4 Actual student response CHARACTER 2 NEXT LOG BLOCK FIXED BIN 15 0 The number of the block in CAIFILES holding the continuation of this student s log information If this is zero it means there is no continuation this is the last block in this student s list x Figure 13 A Block of a Student s Log Information 40 As mentioned before each of the regions 11 through 1499 may be called upon to hold different kinds of information at different times Consider a contrived example Assume that region 476 currently holds the LCB for a particular lesson in some author s library Suppose that author signs on to the system and requests a PURGE of that lesson The AUTHOR procedure would cali ACBPROC to remove the lesson from the author s directory Since the lesson is to be purged its LCB is no longer needed Region 476 would then be rel
106. to AUTHOR adding a lesson and returning to AUTHOR the region number allocated for its LCB returning a formatted list of all of the lessons owned by the author now signed on and search ing the ACB directory to see whether a given author id num ber occurs there 5 The ACB is brought into core and hence enqueued for the duration of the procedure Error conditions which ACBPROC discovers are coded and returned in a parameter 2 7 COSPLER COMPLER is called by AUTHOR with a single DIAL source Statement to parse The main compilation loop receives tokens from SCAN the internal lexical scanner COMPLER in turn calls CODEGEN just before a reduction takes place to emit object code instructions into the TEMP structure Upon return to AUTHOR those instructions and literals are then appended to the appropriate system files The code genera tion phase then is external to COMPLER COMPLER is essen tially just a parser COMPLER attempts no error recovery as soon as it discov ers an error it returns to AUTHOR with a diagnostic message Stored in TXT and LP holding the place in the statement which COMPLER thinks is in error The emphasis was placed on diagnostic intelligence not recovery 2 8 TABLES No computing is done in TABLES it merely contains the parser recognition tables for COMPLER This nodule merely declares and initializes then The tables are produced by the compiler generator PLICONST Because the tables are dec
107. wo categories First any access to a shared file causes that file to become enqueued no other access may occur until a dequeue operation has been completed This is true whether the access request comes from the on line system or from an off line program Second a general protocol for taking backups of all datasets has been established 8 1 USING THE OS ENQ AND DEQ FACILITIES The CAI System module EQDQ calls the CHAT system rou tines ENQ and DEQ which serve as interfaces between CHAT and the OS ENQ DEQ Supervisor Macros EQDQ has several entry points3 each of which serves a various eng deq func tion l There are eight serially reusable resources defined in CAISYSTEM but some do not exist at times They are divided into three groups i The first group always exists It consists of the first four blocks of CAIFILES which contain data Shared by several of the routines Resource 1 MAINFILE Resource 2 CCB Course Control Block Resource 3 ACB Author Control Block Resource 4 FBL TOP Free Block List top 2 The second group of resources exists when the on line System is running and an off line program is in exe cution as well Basically it prevents an off line program from changing an author related file while an author is signed on changing a student related file while a student is signed on etc Resource 5 CAISYSTEH anyone signed on Hem D Ama GP HMM GNU AND UD NND RUD KON ue Kp GU ATP m AO ee 3 See
108. wo of the design decisions seem to have created needless restrictions in the handling of the lesson files Hore important I believe is that NHudge s full design was isplemented and the omission of several features from the final version of the system rendered it awkward and impractical to use And finally since Hudge Chose to implement his own author language rather than use a general purpose language already existent he autonmati cally incurred the expense and overhead of writing what is essentially an interactive compiler for that language and imbedding that compiler into the system Now writing a bad compiler is a sizable task writing a good one is an enor mous task and in my judgment the DIAL translator lies some where between the two extremes In any case it does not give its user the kind of support to which many have become accustomed The uninmplemented features of the CAI system were primar ily features of the author language The control structures of DIAL are basically those found in PL I with a few major extensions Therefore the DIAL architecture defines the IF THEN IP THEN ELSE and DO WHILE statements all of which are seaantically defined as in PL I None of these three was actually implemented in the systen Consider for a moment their use in a response analysis situation by exa mining the following possible uses IF ae had expected answer THEN SHOW Wrong answer try again ELSE SHOW Y
109. ysten SINCLUDEd members ARECDEF ACBDEF EQDQEXT Procedures called INIT EQEXT DQEXT Reference Section 3 3 CAILOG prints a log of all student activity since the last run of CAILOG clears the logfile blocks on file CAIFILES INCLUDEd members MAINDEF LOGRDEF EQDQEXT Procedures called FREEBLK HEADER INIT EQEXT 4 DOEXT Reference Section 4 4 1 CAIREST restore CAIPILES recover resume dump status from tape backup XINCLUDEd members MAINDEF SCBDEF PLIDEF PL2DEF SRECDEF EQDQEXT Procedures called FREEBLK INIT EQEXT DQEXT Reference Section 6 3 CCBMAINT iaserts deletes courses to from the Course Control Biock and hence the System XSINCLUDEd members CCBDEF EQDQEXT Procedures called INIT EQEXT DQEXT Reference Section 4 3 2 CHECK displays a please cancel message to the console This is the first step of each of the CAI daily jobs but is overridden by proper execution This prevents unauthorized users from running the daily jobs Reference Section 7 3 5 62 10 11 12 13 14 15 DIRECTRY prints a directory of all students in the Systems complete with personal information X INCLUDEd Resbers SRECDEF Procedures called HEADER Reference Section 2 4 2 DJCYMNT alters the Daily Job Controi Command Vec XINCLUDEd members MAINDEF Procedures called HEADER INIT EQEXT DQEXT Reference Section 4 3 1

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