Class A2 IGCSE Computing Chapter 32 Number Bases
Contents
1. Client Server Computing Expensive computer can be made available to a lot of users Client stations can update the data Consistency is maintained because only one copy of data is preserved The DB processing is done by server with client only displaying the results Communication time between DB and Client is minimized because only results are sent back Object Oriented Databases Object Oriented databases were designed so as to be able to store Objects Not only numbers and characters but also drawings images photographs video voice Chapter 51 Database design and Normalisation Diagram of DBMS in an office to get a reference point Brief of how a table looks like how a structure of tables look like how they are related What is a relational database 43 What is a key primary key foreign key Normalisation What is it is a process to come up with the best possible design for a database Why needed we will understand after we do the rules Example Company Department Employee First Normal Form Department and Employee in one table not in any normal form Discuss why this is not good Design this in First Normal Form Company Code Department Code Name Emp Code Empl Name Emp DOB Manager Code Manager Name Split the Department and Employee table Department will have Employee Number Employee Table will also have Employee Number A table is in First Normal Form if it contains no repeating att2. a calculator program that is executing a very complex task and is taking time Now if you want to provide a feature whereby you want the application to be able to stop when a button is pressed such a feature is provided by means of threading Allocating job priorities 35 The scheduler will be responsible for allocating job priorities and to assign a number which will determine what job will run when Scheduling objectives A scheduling policy should try to 1 Maximize throughput try to process as many jobs as possible in as little time as possible 2 Maximize the number of users who can work optimally quickly and achieve good response times 3 Balance the resource use if for example a printer is idle a high priority could be given to a job using the printer 4 Give priority to jobs based on how long they have been waiting as well 5 Achieve a balance between response time and utilisation of resources Criteria used for scheduling 1 How much I O a process needs 2 How much CPU time a process needs 3 Whether the process is batch of interactive 4 How much more time a process needs to complete or how big a process is 5 How important is fast response for this job Deadlock of jobs one resource is waiting on a resource that the other job is using and vice versa Chapter 49 Memory File and I O Management Objectives Why is memory management needed 36 1 To enable different proc
3. do some disk I O so an interrupt is generated The interrupt handler changes A to blocked makes a request to the disk drive to get data and invokes a program called the dispatcher which selects Job B to run next Sometime later the disk drive fills up the buffer and says it is ready Program A is now changed to runnable by the interrupt handler One millisecond later the status of B is changed to runnable and the processor hands over the CPU to A Chapter 50 Database Concepts Diagram of DBMS in an office to get a reference point Traditional File Approach e Data Redundancy e Data inconsistency 39 40 e Program Data independence adding fields change in format e Lack of flexibility non routine report assimilate data takes time e Data was not shareable across departments Database approach Database collection of non redundant data shareable between different apps Unproductive maintenance programs were still dependent on the structure of the data so that when one dept needed to add a new field to a file all other programs accessing that file needed to be changed Lack of security All data was accessible by all apps Database Management System DBMS e Allows for program data independence whereby the storage structure of the data is hidden from the user e Restricted user access to data provides for security 3 level architecture External or user schema individuals view o
4. level packet network destination address is checked and the packet is then sent to the appropriate network Routers can also enclose the packet in another packet and initiate the transfer through a new route by assigning another address BRIDGES These connect two segments in a network environment Bridge learns where the nodes are located and will send the packet to another node if necessary or the comp to which the packet is intended if the comp is on the same segment Chapter 60 Wide Area Networks They connect together geographically remote computers 2 options of communication over a WAN Dial up networking User connects to the WAN using a standard telephone network Dedicated or leased lines User s computer is permanently connected to the WAN Value added networks A privately owned wide area network that provides a specific service not readily available on public networks but managed by a third party Like Cloud Computing The VAN is set up by a firm that is charge of managing the network They then sell subscriptions to other companies and charge a fee to use the network 66 Electronic Data Interchange Transmission of business data from one computer system to another computer system via a wide area network Security Keys Encryption Connecting to a wide area network 1 67 Use of a dial up telephone line and a modem Modem speeds vary and is typically 56Kbps ISDN modem is not requi
5. special purpose requirements Type of System batch online real time 50 Files contents record layout organization and access methods Processing the programs and procedures needed and their detailed design Security how to secure the data from accidental corruption or deliberate tampering or hacking Testing strategies well tested before going live Hardware selection of an appropriate configuration Prototyping Prototyping is a useful design tool It involves building a working model of a system in order to evaluate it test it or have it approved before building the final product Throwaway prototyping where prototypes are discarded before the real system is started Evolutionary prototyping where prototypes are developed into a working system The prototyping model falls under the spiral model as opposed to the waterfall approach to systems design 51 Systems flowcharts When a systems analyst is developing a new computer system his or her ideas will need to be written down A flowchart diagram showing the various tasks will go a long way in conceptualizing the system Flowchart would have Tasks carried out Devices used hdd tapes Input output media Files used Symbols used Process If branching 52 Storage User Interface User Interface design refers the the technique of creating a screen that is easily used by the user he can easi
6. 0 30 0001 1110 0000 1010 10 Chapter 33 Floating Point Numbers 0 5 0 25 0 125 0 0625 1 2 1 8 1 6 Two decimal places in Decimals can hold even 1 paisa of a rupee discuss what 2 decimal places in a binary can hold 0 5 0 25 0 75 Floating point binary Consider a decimal 12000 can be written as 12 1045 Similarly binary 110 1 can be written as 0 1101 243 Floating point binary is made up of a sign bit mantissa 9 bits and exponent 6 bits Example 1 O 110100000 000011 0 1101 243 110 1 Binary 1 Place the point between the sign bit and the first digit of the mantissa 2 Convert the exponent to its equivalent decimal or 3 Move the point right if the exponent is ve or left if exponent is ve the appropriate number of places 4 If the Mantissa is negative and the exponent is negative move the decimal point to the left adding ones Else always add zeroes 5 Convert the resulting binary number in denary Eg 2 Now consider the binary split into sign bit mantissa 9bits and exponent 6 bits 0 100000000 111110 This is 0 1 24 2 0 001 That is 1 8 or 0 125 Eg 3 1 11010000 000011 1 1101 2 3 1110 1 If the first digit is a 1 it is a negative number 8 4 2 0 5 1 5 Note The leftmost bit has a negative place value Eg 4 This is the correct implementation 1100000000 111110 es 22 111110 complement 000011 2 1 111 1 0 5 0 25 0 125 12
7. 5 Normalization Consider 1234000 can be expressed as 01234 10 8 or 1 234 10 6 or in a normalized form as 0 1234 10 7 Similarly for binary numbers using a mantissa of 9 bits plus a sign bit the number 0 000001001 would be represented in the mantissa as 0 100100000 with an exponent of 111011 5 Positive numbers are normalized by getting to the first bit 1 of the mantissa not counting the sign bit and adjusting the exponent accordingly Eg 0 000110101 000010 Step 1 0 0001101 Exponent 2 Step 2 0 110101000 Exponent 1 Answer 0 110101000 11111 Negative numbers the normalized form is where the first bit of the mantissa not counting the sign bit is O Eg 1111100100 000011 Step 1 Insert the assumed binary point to the right of the sign bit 1 111100100 Exponent 3 Step 2 Shift right 4 places so first digit is a O 1 00100 Exponent 3 4 1 see here the 1s are expendable since this is a negative binary Answer 1001000000 111111 Advantages of Normalized numbers Max precision for a given number of bits Only one representation for a given number Chapter 34 Structure and Role of the Processor The processor consists of 3 main units ALU where Arithmetic amp logic operations are carried out Control unit coordinates the activities taking place in the CPU memory and peripherals by sending control signals to the various devices The system clock which generates a continuous seq
8. All PCs share a common cable Works well if the channels are not too heavily loaded Advantages 1 Easy and inexpensive to instal 2 Easy to add more stations without disrupting the network Disadvantages Main cable goes down whole n w goes down Network performance degrades when there is heavy load Example Ethernet Ring Network Computers are connected together There is no central computer and no common cable Messages are passed around the ring in one direction only Advantages There is no dependence on a central computer or file server and each node controls transmission to and from itself Transmission of messages around the ring is relatively simple with messages travelling in one direction only Very high transmission rates are possible Disadvantages If one node breaks down n w breaks down Example Token Ring Operation of the networks Bus open book for diagram draw on board 63 All computers are connected together in a straight line When a computer has data to send it is first addressed it then breaks it down into packets and sends it across the network as electronic signals The computer to which it is addressed will accept the data Note that this system may have several stations sending data at the same time This results in a collision which has to be resolved One method is called CSMA CD in an Ethernet CSMA CD stands for Carrier sense multiple access with collision detection Here the
9. Baseband Carries one signal at a time A bit value of a 0 or a 1 is sent by the presence or absence of a voltage in the cable For short distances only Like LAN Bandwidth is dedicated to one data channel Very fast Broadband Carries multiple signals on a fixed carrier wave with the signals for O and 1 sent as variations on this wave WANSs usually use broadband It is faster than using a telephone line and modem Simultaneous transmission of video voice and data is possible in broadband Synchronous data transmission Timing signals are used to transmit data Start and stop bits are NOT needed Speed is higher because of this but there may be more errors Used for LANs usually Time Division Multiplexing A multiplexor joins more than one data stream into a single stream of data that can be transmitted over a communication channel At the receiving end the demultiplexor separates the single stream of data into its separate data streams Communication happens with time slots being transmitted Time slots can be transmitted with or without data Data is secondary time slots are sent regardless In TDM many data streams share a single line Each data stream is assigned to a time slot Many users can thus carry on conversation simultaneously on a TDM line A TDM line which caters to 3 data streams must be at least 3 times faster than the 3 lines combined otherwise whats the point Circuit Switching 59 When a call
10. Class A2 IGCSE Computing Chapter 32 Number Bases and Representation Denary Number System 100 10 1 5 8 3 Binary and Hexadecimal Number System Binary 32 16 8 4 2 1 0 1 0 0 1 1 19 To convert to Binary put it under respective heads Class HW Or divide repeatedly by 2s To convert to Hexadecimal take the Binary and group it into 4s 0001 0011 1 3 16 1 1 3 19 Translate back to Denary put numbers under the respective heads Representation of negative numbers using 2s complement 2s complement is used to represent negative signed integers Consider number 12 Represent this as 2s complement or 12 1 Take 12 and convert to Binary 8 bits 0000 1100 12 would be 11110100 The one in the beginning denotes it is a negative number Rules 1 Flip the digits and add 1 Or 2 Starting from right leave all the digits alone upto and including first 1 Change all the other digits Converting 12 to 12 is also similar 11110100 12 0000 1011 1 00001100 12 Or leave all digits alone till first 1 Change the rest Converting a 2s complement into Denary Consider this number 1001 0111 Put it under the respective heads here and get the resultant Denary number 128 64 32 16842 1 1 00 10111 This equals 128 16 4 2 1 105 Binary Subtraction To convert the number to be subtracted to a negative number then add it Consider 30 20 First convert 20 to 20 20 0001 0100 20 1110110
11. The web server will handle all details on loading the form and handling the form for use in an application ASP script example lt html gt lt body gt lt form action demo_simpleform asp method post gt 73 Your name lt input type text name fname size 20 gt lt input type submit value Submit gt lt form gt lt dim fname fname Request Form fname If fname lt gt Then Response Write Hello amp fname amp lt br gt Response Write How are you today End If gt lt body gt lt html gt POST and GET Post will send data to server and will be invisible to the user as request is sent via an header Get will send data and will be visible to the user as request will be sent as part of URL Use GET during development for debugging purposes although in ASP NET it s also easy to see what has been sent through POST if you want your visitors to be able to bookmark the submitted pages if you want to refer to submitted pages using hyperlinks Use POST for forms with password fields for large forms or forms with large text fields Please note that web forms in ASP NET use POST by default It can be changed into GET but only for small forms Telnet Telnet is used when you want to get into another computer and work on it remotely It is a terminal emulation program t is used to remotely control servers When you work from home you will use this a l
12. antages over CUI They use more main memory and hard disk space They require a more powerful processor and a better graphics display They are slower while executing a command because much more interpretation takes place They can be irritating to use for simple tasks because a greater number of operations is required Operating System Functions 1 Process management 2 Memory management 3 1 0 Control 4 File management The Process concept A Process is a program in execution A process may be in any one of 3 states 1 2 3 A process is running or current if it is actually using the CPU A process is runnable or ready when it could use the CPU when itis available A process is suspended or blocked when it is waiting for I O and could not use the CPU even if it were free Process Control Block PCB Threads 34 When a process is interrupted it saves the place where it needs to resume next time it is started in a structure called the Process Control Block This will contain the following information Process_id Current_process_state Job_priority or other scheduling information Program Counter Register save area A pointer to the processor s allocated memory area Pointers to other allocated resources CPU time used so far Estimated time to completion Links to other PCBs A thread is a part of a program that is run asynchronously and the rest of the program continues on its path Consider
13. are accepted into the DB If not available a Rejection letter goes to the student Level one DFD Only show In and Out items with Inventure System as a central DFD unit Level two DFD Show complete Details in the diagram Entity Attribute Modelling The system database designer DB Architect produces a conceptual design identifying the various entities and attributes and showing how these are related E R diagrams are covered in Chap 22 Data Dictionary It stores data about data It stores names of data items fields or variables data types length validation criteria and other chars such as usage physical representation ownership authorization and security Object oriented Analysis Diagrams When designing a system that is going to be programmed in an object oriented programming language the analysis must include which methods act on these classes See Chapter 38 for Class diagrams Volumetrics Volume of data affecting the system 1 The number of input documents or on line requests into the system 49 2 Number of users and whether online or batch processing is required Chapter 55 Systems Design Development and Testing The Waterfall Model to Systems design Systems Designer will consider the following Before u start a system Output content format sequence frequency medium Input volume frequency documents used input methods User interface screens and dialogues menus
14. arts E R diagrams Class diagrams 4 Overall system design showing the component parts and data structures 5 Data dictionary 6 Algorithms 7 Clearly annotated program listings 8 Configuration settings Chapter 57 Input and Output Methods Input devices Scanner used in scanning documents photos Can scan black and white as well as color Resolution is measured in DPI dots per inch Three passes is required for color scanning one each for each filter Rewd Green and Blue The scanner shines a bright light on the document and the scan head moves from top to bottom The scan head passes over a line and collects data by measuring the intensity of light that is reflected back from the document Touch Screens These are used in industrial environments such as manufacturing wareohousing and security systems Also avionics and medicing And of course phones For every day work in the office it is less useful as it becomes very tiring to use the touch screen Different sensor technologies would be 1 Responds to pressure 2 Aplastic screen on top of the existing glass surface Conductive coatings are applied to the inner surface of both elements Magnetic Ink character recognition MICR is a character recognition technology used primarily by the banking industry to facilitate the processing of cheques The technology allows computers to read information such as account numbers off printed documents Unlike barcod
15. ayed on a computer Somethings Wore Baseband A baseband signal or lowpass signal is a signal that can include frequencies that are very near zero Used for Ethernets LANs Very fast Broadband A signaling method which can include or handle a wide range of frequencies Compare broadband baseband Broadband is like cable television Multiple channels can be submitted simultaneously in Broadband Used when sending large amounts of data over a wide area where wait times can be unacceptable Baseband signaling would be sending only a single signal over the cable This type is used in Ethernet networks They are simple and fast Chapter 61 Internetworking Internetwork is the connection between networks Best known internetwork is an Internet Routers a device that forwards packets between networks using IP addresses Routers use headers and forwarding tables to determine the best path for forwarding the packets and they use protocols such as TCP IP to communicate with each other and configure the best route between any two hosts It uses a combination of network and node address to communicate with each other 68 Gateways a device used to connect networks using different protocols It repackages the data so that it can be read correctly at the receiving end It is also called a protocol converter A gateway acts as a conversion from one protocol to another or in the case of VoIP from the VoIP network to the POTS netwo
16. cket arrives at a router the router examines the IP address put there by the IP protocol layer on the originating computer The router checks it s routing table If the network containing the IP address is found the packet is sent to that network If the network containing the IP address is not found then the router sends the packet on a default route usually up the backbone hierarchy to the next router Hopefully the next router will know where to send the packet If it does not again the packet is routed upwards until it reaches a NSP backbone The routers connected to the NSP backbones hold the largest routing tables and here the packet will be routed to the correct backbone where it will begin its journey downward through smaller and smaller networks until it finds it s destination Chapter 64 HTML and ASP 70 What is FTP FTP works by opening up a channel for communication and then staying open till you end the session You then type in commands to get files from the site and or put files into the site Someone opens up their server for the world to communicate textually with them Open ftp co in will open a ftp connection Typically you will enter the userid and password after doing this If it is an anonymous ftp site no user id and password will be asked Then u will type in commands like put and get or mput and mget to work with files Exit will end the session Go to this anonymous ftp site to browse ftp www i
17. computer checks to make sure channel is not busy before sending data If busy it has to wait before sending data Once it begins transmission it has to listen to other nodes before beginning transmission If there is a collision both stations will have to wait a random period before trying again What is a segment Itis a run of cable to which are attached a number of workstations What is a bridge It connects two segments in a network A bridge will memorise addresses and assign a frame to the appropriate sement It will also amplify the signal so that the network is faster What is a hub It is used to connect together computers in a network in a star fashion What is a switch Intelligent hub used to directly deliver data to another computer on the network What is a Repeater A repeater is used to amplify signals when the cables get lengthy This takes some time so care needs to be taken to make sure there are no network data drops Ring Network Computers are connected in a ring Signals travel in one direction only in a ring network 64 A small packet called a token is passed to each computer If the computer has information to send it will modify the token add address information and sends it down the ring The information passes around the ring until the token reaches the destination Disadv If one node fails the whole network will go down STAR Here computers are connected to each other through cable segm
18. ents to a central hub When a signal is sent from a computer it is received by the hub and then sent across each segment to the other computers connected to the hub Only the computer it is addressed to acts upon the data When a computer in a star network fails it does not affect the other computers except when the failure occurs in the hub Switched Ethernet Ethernets have a maximum length for operation 500 m Hubs repeaters can be used to extend the Ethernet and then the Ethernet can extend to a maximum of 2500 mts Switches are intelligent hubs which deliver packets directly to the destination without having to try delivering to each computer in the network This also eliminates collisions Server based network A network where resource security and administration and other functions are provided by dedicated servers Windows 2000 Server Peer to peer networks A network where all computers have equal status There are no dedicated servers MS Windows 2000 E rorm the Notes LANs use digital signals to transfer data between nodes WANs can use digital signals in a local network but will use the analogue signals to transmit over the internet 65 Different types of cables are used for different purposes Coaxial Shielded Twisted pair and Unshielded Twisted pair are some types of cables used in network connections SWITCHES are used for wired networks Higher performance Not for WANs ROUTER Router receives the network
19. er dials a number the path between the two telephones is set up by operating all of the exchanges involved in the path The circuit remains on continuously for the whole call The two devices must transmit and receive data at the same rate There is no time or resource wastage to reconstruct messages A leased line can be used if electrical interference produced by switching is a hindrance to data transmission between 2 computers Easier to hack into and listen in on calls electrical interference can be a problem for data transfers using circuit switched networks PSS is cost effective as cost depends on number of packets sent more likely to be affected by network failure as PSS can send along different route Packet switching In a packet switching system messages are divided into packets of 128 bytes each Each packet contains 1 Source and destination address 2 A packet sequence number so that the whole message can be correctly reassembled 3 Achecksum for the purpose of error checking Datagrams In TCP IP a packet is called a datagram The network takes a packet and redirects it down to the next node along its way to the destination The Packet Switching system PSS ensures that all the packets are re assembled correctly at the destination The internet is a PSS system PSS can also store packets until the node is ready to send it it can also do some error checking and correction whereby when a node has an error it
20. eritance take a class and inherit from it to obtain its defined properties and methods Encapsulation hides data methods Polymorphism same name method What are Objects and Classes Class a set of objects that share a common data structure and common behavior CarClass Fields Methods Steering Start and Continue Till Stop Accelerator Clutch Tyres Objects Sports Car Methods Additional Field Start Continue Faster Till Stop 18 Alloy wheels Containment diagram for a GUI Event Driven programming Benefits of OOP 10 1 2 4 5 Data is protected and only accessible in well defined ways Re use of objects become possible Specialists designed objects are more reliable Confusion in the way of multiple functions existing to do similar tasks is avoided Time Saving Consistency in design and implementation Chapter 39 Prolog Programming What is a procedural language Define Something that follows a sequence starts of from declaration of variables to opening up a file processing the file doing other things with the data it has read and then closing the file followed by printing a report of what it found What is a Declarative language A declarative language does not follow a sequence It can be written in any order It consists of Facts Rules Goals and Queries Fact A fact consists of a predicate programmer defined and zero one or more arguments Eg male Jo
21. es or similar technologies however MICR codes can be easily read by humans The use of magnetic printing allows the characters to be read reliably even if they have been overprinted or obscured by other marks such as cancellation stamps and signature Optical character recognition usually abbreviated to OCR is the mechanical or electronic translation of scanned images of handwritten typewritten or printed text into machine encoded text It is widely used to convert books and documents into electronic files to computerize a record keeping system in an office or to publish the text on a website Optical Mark Recognition OMR is used for grading answer sheets after exams Students are asked to darken the circles with a pencil to mark the answer they choose Many traditional OMR Optical Mark Recognition devices work with a dedicated scanner device that shines a beam of light onto the form paper The contrasting reflectivity at predetermined positions on a page is then utilized to detect the marked areas because they reflect less light than the blank areas of the paper OMR does not require a complicated pattern recognition engine unlike OCR Chapter 58 Networking Methods When a network is formed using physical cables over shorter distances they form a LAN When a network comprises a wide geographical area and uses telephone lines or specialized digital communication lines they are part of a WAN 58 Modes of Network Operation
22. esses to be executed concurrently Allocate appropriate memory resources 2 To protect processes from each other when they are running together 3 To enable memory sharing of memory space when required 4 To make the addressing of memory space as transparent as possible A Loader loads the process program that needs to be executed Absolute loader loads the program into a fixed area in memory It is fixed at compilte time and the program will work only if the program is loaded at that specific area in memory Relocating loader loads the program anywhere in main memory and all addresses subsequently are relative to the start address The start address is loaded into a special register called the base register There are again 2 types of relocation Static Relocation Once loaded into a position it cannot be relocated again Dynamic relocation Once loaded into a position it can be relocated again This is necessary for multi programming OS This is made possible by not replacing any logical address references with physical addresses The logical to physical mapping is done at run time by 37 the hardware Memory Management Unit MMU using base register addressing Virtual Memory memory on hard disk where pages of program and data are stored temporarily It makes believe that the computer has more physical memory than it really has Main memory is divided into fixed size blocks typically 4K called frames Each pr
23. ete_Item Begin Get item to delete Call Findltem to see if item is in list and to return position if found If found false then write error message Else While p lt size 18 19 item p item p 1 p pt 1 Endwhile size size 1 end if End procedure Chapter 42 Linked Lists A Linked list is a data structure used to hold a sequence Each item is called a node and it contains a data field and a next address field which is also called a node or a pointer A Linked list also has 2 additional pointers start pointing to the first element of the list nextfree pointing to the next free element of the list Algorithm to insert an item into a linked list Consider this list start 1 nextfree 5 Address Name Pointer node p pointer node p name 1 B 4 2 T 0 3 J 2 4 C 3 5 6 6 7 7 0 To insert M Put Min 5 M goes before T gt so M pointer should point to T M goes after J gt so J pointer should point to M nextfree should be 6 Begin process Node nextfree name newname P start now get into a loop follow pointers until node p pointer points to a name gt newname this should lead u to J whose pointer points to T which is gt newname temp nextfree which is 5 nextfree node nextfree pointer it will set nextfree to 6 node temp pointer node p pointer M pointer will be set to 2 node p pointer temp J pointer will be set to 5 End p
24. evices using an I O bus Each I O device has a hardware controller unit attached to this bus system which can transmit data to or receive data from main memory Each device sends an interrupt signal to the processor when it has completed its task Device Driver Breaks down a user request for an I O device to do something into a series of sub tasks Like check if the disk is present and active locate the space for the file on the disk position the read write heads at the appropriate write location all needs to be done to save a file to disk Interrupt Handling An interrupt is like an event in event driven programming When the CPU needs to tell the I O device something it will have to send an interrupt When the OS is ready to service the interrupt it will save the state of the interrupted process and passes control to the appropriate routine Types of Interrupts a Interrupts by the running process say to perform I O obtain more storage b I O interrupts are initiated when say an I O operation is over an error has been detected or say when a device is made ready c Timer interrupts when say a time has lapsed and it is now the turn for another process to run d Machine check interrupts malfunction of hardware e Program check interrupts caused by errors within the program like say reference to an object not in scope Example of an interrupt mechanism Program A is running It requires to
25. executed Testing each part of the system is sometimes referred to as unit testing Black box testing functional testing Black box testing is carried out independently of the code used in the program The system is considered to be a black box and test data is created from the specifications White box testing structural testing This is dependent on the code logic and derives from the program structure rather than its function In white box testing you cannot test what isn t there Before release Unit testing 54 Module testing Subsystems collection of modules System Integration testing Acceptance testing User Acceptance Testing User testing Alpha testing done by the software developers inhouse testing team Beta testing giving the software almost in completed stage to a set of outside users who will now use the system as well as test and report any defects Chapter 56 Implementation Evaluation and Maintenance Implementation This is a stage where people begin to use the new system There are several tasks before the changeover is complete Install the hardware Install the software Creation of master files Data for all master files will need to be entered before the new system can be used Eg Faculty data Student data Choices when converting from an old system to a new one Methods of conversion Direct changeover Adv No data duplication fast and efficient Disadv if problems occur b
26. f DB Conceptual or logical schema over all view of db including entities attributes and relationships Internal or storage schema How the data is stored in the db What sections it uses etc Functions of the DBMS 1 Data storage retrieval and update 2 Creation and maintenance of data dictionary 3 Allow and resolve issues while sharing the db 41 4 Backup and Recovery 5 Security Multi Access DB a DB which allows more than one user to access the DB Ensuring Integrity of the DB Example of 2 users trying to access the DB at the same time One user could potentially override other users data Locking paradigms 1 Open the entire DB in exclusive mode 2 Lock all records in the table being modified 3 Lock the record currently being edited 4 User specifies no locks it is upto the software 6 Open a table in Read Only mode Deadlock User 1 has X lock on record 1 User 2 has X lock on record 2 User 1 requests Read on record 2 User 2 requests read on record 1 Waits Waits Avoidance 1 Abort one 2 ensure that records are modified in same sequence No user calls up record 2 before record 1 Security Basics groups users userid password encyption 42 Access to specific objects in the DB Open Systems ODBC Open systems allow for portability VB to Oracle Sybase is possible using ODBC drivers Excel can also use ODBC to connect to Oracle and store results within itself
27. he primary key is a fact about the key the whole key and nothing but the key so help me Codd For a relation with one candidate key 3NF and BCNF are equivalent A table is in BCNF if and only if every determinant in the relation is a candidate key 45 Now we go back to WHAT IS A RELATIONAL DATABASE A collection of tables where relationships are modeled by shared attributes Foreign Key an attribute in one table that is a primary key in another table Chapter 52 Querying a Database SQL Structured Query Language Used to get information from a set of tables in a database grammar of queries in computing it is also used to input data into tables create tables maintain them and so on Asking questions from the DB is called DML 1 Select 1 col from 1 table 2 Select 2 cols from 1 table 3 Introduce Distinct 4 Introduce Where clause 5 Introduce conditions in a where clause 6 Specify a sort 7 Group By when you need a SUM 8 Extracting from more than one table Chapter 53 Data Definition and Data Manipulation DDL a language to define the structure and instances of a database Create table Employee Emp ID int not null primary key Name varchar 10 not null 46 HiredDate DATE Salary CURRENCY DML asking questions from DB is DML also it allows for manipulation of data in the database Insert into employee emp_id name values 1122 Anand Update employee set name Raj
28. he system against preset criteria 3 Errors which were made during System development 4 Unexpected benefits and problems Software maintenance Three categories Perfective maintenance The system could be made better in some way without changing its functionality For example run faster or produce reports Adaptive maintenance Changing needs in a company may mean changing system to adapt For example a single user system can be changed to a multi user system Corrective maintenance Involves correction of previously undetected errors Commercial software programs like Word Excel have bugs in them and maintenance releases are regularly brought out Factors affecting maintainability can skip this 1 Law of continuing change programs in real world environment must change 2 Law of increasing complexity changes will make it more complex 3 Law of large program evolution Evolution is self regulating System attributes such as time between releases size and the number of reported errors are approximately invariant 4 Law of organizational stability Over the programs life its rate of development is approximately constant 5 Law of conservation of familiarity Over the life of a system the incremental change in each release is approximately constant Maintenance Systems documentation 1 Requirement specification 57 2 Hardware and software specification 3 Design diagrams such as DFDs System flowch
29. hn bigger elephant donkey animal reptile large crocodile Atom start with a lower case letter They can contain numbers letters and the underscore EXAMPLE Ajay m Aditi Brad m Bindu Tarun l e Soumya Simi facts male ajay male brad male tarun female aditi 12 female bindu female saumya female simi parent ajay bindu parent aditi bindu parent ajay tarun parent aditi tarun parent brad simi parent brad saumya parent bindu saumya parent bindu simi rules mother m x parent m x female m father f x parent f x male f grandparent g x parent g p parent p x brother x y parent z x parent z y male x not x y sister x y parent z x parent z y female x not x y Does simi have a sister sister x simi X Saumya mother x bindu X aditi 13 brother who simi no Entering items in a Prolog database You can enter items in a Prolog database using the keyword assert Assert is also called a predicate built in in Prolog s built in database and succeeds by asserting its argument Not and listing are other built in predicates assert carnivore lion assert eats X meat carnivore X Rules A rule is an IF condition in Prolog which is used to extend facts Consider bigger bigger bigger bigger elephant horse horse donkey donkey dog donkey monkey _ _ If one asks b
30. igger elephant monkey Prolog will respond with No Because there is no fact that state this Still we know it it true because of the transitivity rule We can define the rule in the program and subsequently it will work is_bigger X Y bigger X Y is_bigger X Y bigger X Z is_bigger Z Y IF logical AND logical OR tests whether 2 things are identically the same _ anonymous variable eg used to find all those people who are mothers 14 Changing facts at run time see page 237 for example EXAMPLE Chapter 40 Recursion In anormal scenario you would define a function and call the function from another place In recursive functions the function is called from within itself Consider the example of a factorial 1 Ifn 1 then Factorial of n 1 2 Otherwise Factorial of n product of n and Factorial of n 1 Int Factorial int n If n 1 then return 1 Else Return Factorial n 1 n Equivalent For loop Result 1 N 10 For i n i gt 1 i Result Result n Recursive functions are evaluated at the time of unwinding Fact 4 4 fact 3 3 facty 2 2 fact 1 1 24 lt 4 6 lt 3 2 lt 2 1 If the recursion is for a lot of numbers then unwinding can result in stack overflow 15 Advantages Non recursive solution is more efficient in terms of computer time and space This is because when using a recursive solution the computer has to make multiple fu
31. inks that connect together computers that are geographically close Type of cabling Twisted pair like the ones found in telephone cabling Co axial is high quality well insulated cable which can transmit data much faster and more accurately than twisted pair Other communication methods Radio waves Microwaves stations should be not more than 30 miles apart because of the earth s curvature and microwaves travel in a straight line Communications satellites A computer is connected to a network by a network interface card which must match the type of network it is connected like Ethernet Token ring and ATM Network Topology How best to arrange the computers in a network has to be thought of before building a network Different topologies offer different advantages and disadvantages Star Network Eg There is a mainframe computer in an office that other computers need access to There is a main server which is very powerful and has an application software which is accessed by different programmers in the office Advantages 1 Cable failure affects one computer only 2 Consistent performance in times of heavy usage 3 More secure Messages cannot be intercepted by other stations 4 Different stations can transmit at different speeds 62 Disadvantages Costly because of cable lengths Distributed star will have many stars and connected to each other with connection boxes Bus network
32. is possible to correct the error and retransmit 60 Virtual Circuits A PSS that establishes the route between sender and receiver before transmission of data packets start Example If computer A wants to send a message to computer B it first sends a Call Request packet to the first node This node decides which node to route the request to and the next node repeats the routing decision until the request arrives at Computer B Computer B now sends a Call Accept packet that retraces the route of the call request packet Computer A can now transfer the message to computer B through this established route Packet Switching vs Circuit Switching More efficient use of lines Cost depends on the number of packets sent not on distance Less likely to be affected by network failure Better security Data is less likely to be intercepted because packets can be sent along different routes or be interleaved with other unrelated packets Asynchronous Transfer mode ATM a packet switching service that transmits data in short fixed length packets referred to as cells using a virtual circuit Standard protocols Protocol pre agreed signals codes and rules to be used for data and information exchange between systems A Standard Protocol is a protocol that conforms to a standard laid down by a standards authority to allow data exchange between any computer Chapter 59 Local Area Networks 61 Local area networks are a set of l
33. ly understand what is in it what information it is requesting It should direct the user on what to do next very clearly It should clearly point out errors in data entry and let the user know where he has made a mistake Basically a good user interface design goes a long way in Systems acceptance and usability of the system 1 Who is going to use the system 2 What tasks the computer is performing 3 What is technologically feasible Program design This involves drawing hierarchy charts and structure charts and writing detailed program specifications This is followed by algorithm design and pseudocode before coding Test Data Select the data that you want to test with Preparing for the test data at design stage is useful because you are thinking about the data as well when you are doing the design 53 Development Development includes coding and testing the program and testing the system as a whole Testing strategies A system must be thoroughly tested before being installed The designer should come up with a test strategy to make sure all parts of the system are properly tested Bottom up testing we will use this Individual programs are tested using prepared test data complete programs are then tested using data which ensures the whole system is covered all routes are tested Top down testing The skeleton of the complete system is tested with individual modules becoming stubs which just displays
34. mtech res in What is HTML Hypertext Markup Language Basically it is a language of tags You need to memorize tags in order to build and HTML document To include logic into an HTML document you will use Javascript or Active Server Pages from Microsoft What do u need to build a web page and show it to the world You need to upload it into a server provided by a third party or build your own server and host it there lt html gt 03 lt head gt 04 05 lt title gt Winter lt title gt 06 71 lt head gt lt body gt lt hl gt Winter Vacation lt h1 gt lt p gt My winter vacation was cold chilly and a lot of fun on the snow lt p gt lt p gt How many days till Spring lt p gt lt body gt lt html gt OR 72 lt html gt lt head gt lt title gt My Web page lt title gt lt head gt lt body bgcolor yellow gt love wikiHow because lt marquee gt lt s the best website in the world lt marquee gt lt img src http www wikihow com skins common images wikiHow_logo_5 gif gt lt i mg gt lt body gt lt html gt Web Server diagram ASP scripts are executed in the server Server side scripting languages include Javascript Perl VB Script and ASP net You build a form put controls into the form use scripting to deal with data and save it into the database and retrieve and show data on forms from database Then you save the form ona Web Server in a virtual directory
35. nction calls storing return addresses and copies of local and temporary variables all of which takes time and space Also the values return addresses are put into a stack during the run and stack overflow will happen if the program runs too long In general if a recursive algorithm is much bigger than a non recursive one then use the non recursive one Chapter 41 Lists Think arrays u can insert or delete items from any point in a list data items may be repeated in a list list may contain any type of object a particular list may contain different object types Colours red green blue indigo violet Class 1 44 0 4 a hj l 23 Definition of a list in Prolog Consider Colours red green blue indigo violet Here the Head is red and the Tail are the others Colours red green blue indigo violet a b is a valid list but a b is not since b is an atom and is not a list Operations on Lists Head List returns the element at the head of the list if the list if non empty otherwise reports an error 16 Tail List returns a new list containing all but the first element of the original list Empty List returns TRUE if the list is empty or FALSE otherwise A recursive procedure to print out a list The procedure keeps on recursively calling the procedure T List not executing the Print statement until the list is empty and the procedure runs to completion when it begins to unwind It thus p
36. ocess logical memory is divided into blocks of the same size called pages Pages reside in virtual memory and are swapped in and out of main memory when required by the process An address of a location in a program is of form p d Where p is number of page d is displacement from top of page Dynamically Linked Libraries DLL Is a pre compiled and linked executable file It is linked to the executable and parts of the DLL are loaded when needed by the main program This saves memory though takes a little more time You put shareable code into a DLL You also put code which is not always needed into a DLL File Management Functions 1 To allocate space on the storage device when a file is loaded and to deallocate space when a file is removed 2 Files need not occupy contiguous space They may be divided OS has to take care of this When a file is updated and new records added these may occupy a disparate location 3 To keep track of allocation units occupied by each file 38 A disk is divided into partitions of logical drives known as volumes in NTFS D E F G etc Each partition is divided into clusters 4kbytes each composed of sectors Each cluster is allocated to a file or a folder or is free A table called the File Allocation Table or FAT details the contents and status of each addressable block on the disk FAT is also stored on disk Input Output Management CPU communicates with I O d
37. ot You can also control servers in the US from a remote location like India or vice versa 74 Chapter 65 Java and Applets Java is a language derived from C and loses the pointer the dreaded data reference in C Applets are written particularly for the internet An applet call can be embedded into HTML code the applet will execute on the client Browsers contain aJVM which help in executing applet byte code Applets do not cannot change anything on the computer so they are very safe lt APPLET CODE Hello class WIDTH 200 HEIGHT 100 gt lt APPLET gt A window will open with the size specified and the applet will execute within that window
38. red as the line is digital in itself A modem is not required instead a network termination device and a terminal adapter are required These are commonly called digital modems They use baseband transmission Another version is called B ISDN uses broadband transmission and is able to support transmission rates of 1 5 Mbps B ISDN required fibre optic cables which is not widely available Cable Modem Cable companies now offer Internet services on broadband transmission using something called cable modems A cable modem can transfer data at 500 kbps or higher compared with 28 8 to 56 kbps for common telephone line modems ADSL Asymmetric Digital Subscriber Line is a technology which turns telephone copper wires into fat data pipes This means that existing telephone lines can provide broadband transmission This requires a special ADSL modem The asymmetric in ADSL refers to the fact that the downstream data rate or the data coming to your computer from the Internet is traveling faster than upstream data or the data traveling from your computer to the Internet Upstream data rates are slower because Web page requests are fairly miniscule data strings that do not require much bandwidth to handle efficiently 6 CODEC a device that encodes or decodes a signal and may compress and decompress these signals in the process For example CODEC can be used to compress video from a video camera so that it can be stored and pl
39. ributes or groups of attributes Second Normal Form A Link table is introduced Employee Number in Department table gets moved there Design this as a Many Many relationship One Emp can be in more than one department one department can hold more than one Emp Employee table still has Manager code Link table Dept Num Emp Num Emp Table Emp Num 44 Dept Table Dept Num Dept Name Mgr Num Mgr Name A table is in second Normal Form 2NF if it is in first normal form and contains no partial dependencies Third Normal Form The Mgr Name in the Dept Table is such that the column is dependent on the Mgr Code which is not a key So there is a non key dependency So move that to a separate table Create an Emp to Manager Link table One emp can have one Manager one manager can have many employees One to Many Is that separate table needed if it is a one to many relationship Put Mgr code in the Emp table and remove the link table keeping the separate Manager table A table is in third normal form 3NF if it is in second normal form and contains no non key dependencies Boyce Codd Normal Form BCNF This is not strictly followed in the Data base modeling world but would like to stress that this is equally important in db design and do not want any of my students to design a table that does not follow this rule The Rule states When a table is in BCNF every attribute which is not part of t
40. rints the list in reverse order Procedure T List If not Empty List Then T Tail List Print Head List End if EndProc Elements of a list may be held in an array Finding an item in a list Inserting an item from a list Deleting an item from a list 1 FINDING Declare an array and write the pseudocode to find an item which is entered by the user in an ordered list Procedure Find_Item Begin 17 variable item to be searched p size found false while item p gt variable p p 1 endwhile when p O the item is not in the list if p gt O then item may be in the list If p lt gt 0 then If item p variable then found true pis the found position item p is the found item end if end if End Procedure INSERTING Declare an ordered array with say 6 items Put the new item in a variable See if the list is full if full display message List Is full Otherwise start at the end of the list and examine each item If value of the last item is greater than value of the new item move current item down one place to p 1 Procedure Insert_Item Begin Get new item variable new item P size If size max then write List is full Else makes space for the new item and finds the correct space While item p gt variable item p 1 item p p p 1 endwhile size size 1 adds in the new item item p 1 variable end if End Procedure 3 DELETING an Item from a list Procedure Del
41. rk A router works by looking at the IP address in the packet and decides if it is for internal use or if the packet should move outside the network In a VoIP conversation you would have a gateway that works for any calls that cannot be carried via IP and it moves them to a POTS connection You generally need both TCP IP TCP is a set of rules used to perform handshake packet sequencing flow control and error handling IP is a set of rules that are used to send packets from one network to another using IP addresses IP address is an address given to a machine on a network in a place Non routable addresses are for intranets Subnet masks These are used to determine the network and the host parts of an address It is a 32 bit number which when ANDed to the IP address will be used to determine which part is the Host and which one is the Network If two computers A and B s IP addresses are like this 192 168 0 4 and 192 168 0 5 then the subnet mask would be 255 255 255 0 which means both the computers are on the same subnet and hence a router will not be needed to communicate between the two comps 69 Chapter 62 The Internet A computer is typically connected to an ISP which in turn connects to the backbone NEP Backbone H amp P Backbone i Ca aI a c Peqmrcal ae Fega EF Backbone Aacksn e Leon Area Lack Aces hetwork Hotani O O C O O Your Computar i Another Computer 1234 SETE When a pa
42. rocess Handling 2 special cases 20 21 1 If list is full At the start of the algorithm you can add If nextfree 0 then Write List is full and exit procedure If you want to insert into an empty list In an empty list pointers will be populated and start will be 0 and nextfree will be 1 1 2 2 3 3 4 4 5 5 6 6 0 If start 0 then Temp node nextfree pointer node 1 pointer 2 Node nextfree pointer 0 node 1 pointer will be set to 0 there are 2 zeros in a linked list one at the position where next item is not there and one at the last element Start nextfree 1 Nextfree temp 2 from statement 1 Else 22 P start End if Deleting an item from a linked list Deleting J 1 Follow the pointers till J is found C 2 Change C pointer to point to T 3 Change J s pointer to point to nextfree 4 Change nextfree to point to J Pseudocode Begin process delete J P start Follow pointers until node p pointer points to the name to delete C is our element that points to J temp node p pointer put 3 in temp node p pointer node temp pointer put 2 in Cs pointer field node temp pointer nextfree put 5 in J s pointer field nextfree temp put 3 in nextfree End process Again here there are 2 special cases If start 0 then write Nothing to delete and exit Start 1 2 Nextfree 3 1 1 B 2 3 2 X 0 3 0 If deletename node
43. start name then temp node start pointer 2 node start pointer nextfree 3 nextfree start 1 start temp 2 End if Print out a Linked List Begin process p start While p lt gt 0 current node p what is the element I want to print print current name the print statement p current pointer next value will be the pointer of current value End While End Procedure 23 24 Chapter 43 Stacks First in Last Out A stack is also implemented as an array Top 3 MaxStackSize 6 6 5 4 3 Anne 2 Millie 1 Charles Procedure Push If Top MaxStackSize Then Write Stack is full Else Add 1 to Top Stack Top Newltem End If EndProc Procedure Pop If Top 0 Then Write Stack is empty Else 25 Poppeditem Stack Top Subtract 1 from Top Endlf EndProc Use of Stacks 1 Evaluating expressions like X A B C D First add A and B and store it in an address Then add C and D and store it Push it on another address in a stack Then retrieve both one by one and multiply and Push it again onto stack 2 Use of a stack for storing the subroutine return address in recursive routines As each sub is called the machine saves the return address of the calling program on a stack This ensures that the sub returns are processed in the reverse order of subroutine calls Chapter 44 Queues First in First Out A queue can be implemented as an array with Fron
44. systems an OS that lets network connections to happen either as peer peer or as a Client Server Client Server systems A network organization in which work stations make use of resources available at one or more servers printer server file server database server application server web server Distributed systems A system in which resources like disk storage and printers exist in separate nodes on a network and users can access these resources transparently as if they are connected to their own machine Chapter 48 Operating System Concepts User Interface command line CUI Job Control Language JCL Graphical User Inetrface GUI Command Line Interface Practice writing some batch files in command prompt Executing of batch files Scheduling of batch jobs Example of a batch job sending letters to students whose books are overdue Job Control Language This is a batch program in a typical mainframe computer where jobs are executed offline based on the JCL job that has been written Priority Error processing Time for the run and Output are all part of the JCL Graphical User Interface The GUI is used to interact with the user in a more user friendly way GUls are typically a slower interface Repetitive tasks are best done using a command line interface than a GUI GUI are aimed towards the novice user Comprehensive online help is also available There is a consistency of layout as well Disadv
45. t Rear MaxSize NumberlnQueue all populated Circular Queue A circular queue is something where elements do not move to front of queue when an item is removed The space is vacant The space is occupied when new elements are added in a circular fashion Procedures for Circular Queue QueueSize 26 FrontP RearP NumberlnQueue To initialize a Queue Proc Initialize Front 1 Rear 6 NumberInQueue 0 EndProc To add an element to a Queue Proc AddElem If NumberlnQueue 6 then Print OverFlow Else If Rear 6 then or Rear Rear Mod 6 1 Rear 1 Else Add 1 to Rear End If Q Rear Newltem Add 1 to NumberlnQueue End If EndProc To remove an element from a Queue Proc RemElem If NumberlnQueue 0 then Print Q empty Else Newltem Q Front Subtract 1 from NumberlnQueue If Front 6 then Front 1 Else Add 1 to Front Front Front Mod 6 1 End If End If End Proc Use of Queues 1 Print jobs waiting to be printed 2 Jobs waiting to be scheduled to run Chapter 45 Trees 27 Chapter 46 Searching and Sorting Searching Algorithm Linear Search Start at beginning of list Repeat Test next item for a match Until item found or end of list reached Binary Search Procedure Binary Search ItemFound False SearchFailed False Top N Bottom 1 Repeat Midpoint Integer part of Top Bottom 2 If A Midpoint ltemSought Then Found Tr
46. tic of a low level language are they are machine oriented and machine dependent 2 Each assembly language statement apart from macros generally translates into one machine code instruction Hence programming is a lengthy and time consuming exercise High Level Languages are written to solve a particular type of business problem Pascal was more general purpose COBOL was for processing files FORTRAN was more for mathematical problems PROLOG was for logic and for Al Features 1 In theory they are portable across machines Java is an excellent example of portability 2 They are problem oriented 3 Generally resemble English sentences C was developed by Dennis Richie at Bell Labs in the USA inn 1972 It was originally developed for systems programming for the operating system UNIX It is a relatively low level language which has many of the advantages of assembly languages At the same time it is easy to learn and can be used like a high level language it is portable and hides the computers architecture from the user Then there is another classification Procedural languages Object Oriented languages Real time embedded systems languages for programming real time systems in Nuclear plants Bomber planes jet aircrafts microprocessor controlled washing machines etc Time based actions something needs to happen in 5 seconds happen every 30 secs and such Chapter 38 Object Oriented Programming Concepts of Inh
47. tion from the user The running of batch jobs is normally controlled by a JCL do an example of a batch script with the students Interactive 31 Here the user and the computer interact with each other User types in commands supplies data and the Operating system responds with results Real Time This is again classified as Process control Information storage and retrieval and transaction processing Processor should not be used to full capacity for most of the time These should respond immediately to input Event based These should not have a time lag of even a few seconds These should be fault tolerant error reporting and things like that are of no use here It has to succeed Examples Nuclear reactor safety system Airbag deployment system in cars A real time system should be able to respond to events happening at unpredictable times and which may happen in parallel Now for the other Classification Single User Single process Multi Programming running more than one program on a machine Multi Tasking running more than one task program on a multi user system Processor will assign time slices 32 Multi User ability to support multiple users as a whole in a networked environment processor will assign time slices Multiple users are able to communicate with the computer at one time Multi Processing Multi Threading Other types of Systems Network Operating systems Similar to Multi User
48. ue get this away with Else If Bottom gt Top Then SearchFailed True get this away with Else main algo 28 If A Midpoint lt ItemSought Then Bottom Midpoint 1 Else Top Midpoint 1 End if End if End if Until ItemFound or SearchFailed End Proc Sorting Algorithm The Classic Bubblesort Procedure BubbleSort Repeat Flag False For Count 1toN 1 If A Count gt A Count 1 then Temp A Count A Count A Count 1 A Count 1 Temp Flag True End If End For 29 30 Subtract 1 from N Until Flag False or N 1 EndProc Chapter 47 Operating System Classification Operating System program that controls the execution of all other programs applications and acts as an intermediary between users and computer What is booting Operating system is held on a disk and has to be loaded into main memory when a computer is switched on before any other programs are run This process is called booting The ROM contains the programs that will tell the computer where it can find the part of the operating system which needs to be loaded first into memory Once this part is loaded more instructions are executed to load the rest of the Operating system needed for the applications programs to run This process is called pulling itself up by its bootstraps or booting Types of Operating Systems Batch In a batch operating system a job runs from beginning to end without interven
49. uence of clock pulses to step the control unit through its operation Registers 32 or 64 bits in size to hold imformation temporarily as it is being processed Program counter sequence control register sequence register holds the address of the next instruction to be executed The general purpose registers are used for performing arithmetic functions In some computers there is only one general purpose register called an accumulator The Current Instruction Register CIR or the IR contains both the operand and the operator of the current instruction The memory address register MAR holds the address of the memory location from which data will be read or to which data will be written The memory data register MDR or MBR is used to temporarily store data read from or written to memory The status register SR contains bits that are set or cleared based on the result of an instruction They also store information about interrupts Chapter 37 High Level and Low Level Languages Low level Languages these are machine oriented They are written so as to extract the maximum usage and minimum storage from the computers processing units and memory A typical example would be a device driver like a printer driver Machine Source Executable code code preprocessing processing Compilation a f Interpreter Source Intermediate TP code code preprocessing processing Interpretation 1 Characteris
50. usiness could be disrupted Parallel conversion Adv Results from new system can be checked against known results New system can be tweaked if errors are present without disruption to business Disadv Duplication of effort could be an issue 55 Phased conversion Used with larger systems where different modules can be implemented in phases Again Phased conversion could be direct or parallel Pilot conversion where a small portion of the organization uses the new system Training for users Moving from old system to a new one would require additional user training Detailed user manuals documentation is finalized before system goes live Training staff is a crucial part of the success of any new system Managers will need to be trained in using the system They should feel confident in showing their staff to perform critical tasks Technical staff will need to be trained in correct backup procedures customization for specific user needs troubleshooting when things go wrong Manuals Installation Manual how and what are the hardware requirements for installing the system P 330 Operations Manual How to operate the system for day to day things Any backups required reports to be generated recovery processes User Manual Using the system Part of training requirements Post Implementation review 1 Systems actual performance vs anticipated performance objectives 2 Assessment of each aspect of t
51. where emp_id 1122 Delete from employee where emp_id 1122 Chapter 54 Analysing a System do with open txt book Parallel to defining the project Systems investigation 1 Feasibility study Hardware feasibility Availability of software Technical know how Tools User acceptance Maintenance requirements 2 Information requirements Complete understanding of the current system and how it will change read Systems Investigation for complete understanding 3 Fact finding methods a Observation of the task b Examine existing documents c Surveys Questionnaires d Interviews Reporting techniques a Where the data originates b What processing is done by whom c Who used the data d What data is stored and where e What output is received and who uses it Data Flow Diagrams P External entity Data source or data destination Process An operation performed on the data Label the process Brief explanation Where the process takes place Data Store File disk tape Data Flow Levelled DFDs 47 48 Sometimes it is not possible to represent the complete business system in one diagram Hence 2 or 3 levels of data flow diagrams may be used each showing more detail Class exercise worksheet Students seek admission into Inventure school Admissions office verifies from their records if the particular class has availability If Available the student is accepted and course details
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