as a PDF
Contents
1. you Connection c nextElement System out println checking you channel mychann if you channel equals mychann amp amp you isGJS System out println serv_str is you serv_str if sendUP 0 amp amp you portnum UPport System out println not sending else if you serv_str equals GeoSheetStd0ut System out println sending you send msg break while public void send2UP String msg int portnum int serv_num Connection you String serv_str Enumeration c connections elements while c hasMoreElements you Connection c nextElement if you myType equals UP if you UPport portnum amp amp you serv_str equals last_ss 39 you send msg public void addChannel String hoststr int portnum String newchannel channelQ addElement new String newchannel hoststr portnum System out println adding to channelQ newchannel hoststr portnum public boolean GJSHasFloor String host int num String serv_str String you Connection connect Enumeration c connections elements while c hasMoreElements connect Connection c nextElement if connect myType equals GJS amp amp connect portnum num amp amp connect hoststr equals host connect serv_str new String serv_str break c floorQ elements while c hasMoreElements you String c nextElement if you startsWith host num r2. GeoJAVASheet and chat box are initiated with the user s user and channel name 11 4 3 GeoJAVASheet The GeoJAVASheet applet is actually a frame that contains 1 a panel onto which users may input graphical objects such as points line segments triangles rectangles polygons polylines circles arcs and various types of graphs 2 a row of buttons on top Return for communication with the user s application program Undo undo the previous action Delete a specific object on the panel Modify an object s component Move an entire object Delete All Quit Toggle Grid reference lines 3 a choice box on the left to select an object to input onto the panel 4 a floor button under the choice box this will be explained later and 5 a row of property selectors on the bottom such as line widths line colors font styles font sizes line styles and fill styles Figure 2 shows a GeoJAVASheet on a Windows machine E GeoJAVASheet 1 0 Northwestern University Electrical and Computer Engineering Depa PI EG HOST geomamos PORT 3809 Return Undo Delete OFF Modifs OFF Move OFF Delete Al _Quit Toggle Grid Nodstaype x do Bae vi Wee B Request Floor You do not have the floor Line Attributes Black fi Text Attributes Courier fiz 7 Line Style Solid Fill Style None 134 Unsigned Java Applet Window Figure 2 GeoJAVASheet Applet
3. fi z Text Attributes Courier z fiz z Line Style Solid z Fill Style None z Figure 3 GeoJAVASheet Application without re writing their code and new users need not download a Java compiler if they do not already have one In the future we plan on incorporating the Computational Geometry Algorithms Library CGAL 13 LEDA The GeoLIB library is based on the basic geometric classes and member functions of the Library of Efficient Datatypes LEDA library currently version 3 5 2 By inheriting from this comprehensive library of geometric classes GeoLIB provides both a complete library of geometric objects as well as several basic geometric algorithms GeoLEDA The visualization portion of the GeoLIB library is contained in the Ge oLEDA library GeoLEDA consists of geometric objects that 1 inherit from the objects in the LEDA library and 2 contain visualization member functions as well as interprocess com munication IPC functions that provide the basic socket infrastructure for communication between the components of the Geo JAVA system It also contains functions that implement 14 basic geometric algorithms This library is developed and used by the GeoMAMOS system However since GeoMAMOS uses UDP all of the IPC functions have been modified to TCP functions due to the reasons explained in Section 2 This is advantageous in that although initializations are slower communication while connected is faster and mor
4. GeoJAVA Sheet is simply a GUI that responds to 1 messages received from MultiServer 12 and 2 the user s actions such as hitting the Return button or requesting control of the floor Internally GeoJAVA Sheet maintains lists of the various geometric objects Any time a new object is drawn on the panel a new instance of that object is appended to the list to which its type corresponds Users may modify or delete objects on the sheet using one of the buttons on the top row Geometric objects can also be displayed and consequently added to the lists based on messages received from the user program These messages are in a specific format to determine the action to take the data object being referenced and the object s coordinates and properties For example if the user s program wants to display a red point of radius ten pixels at location 25 30 then the message would look like IPC_WRITE GEOPOINT 25 30 10 RED Once the message is received it is parsed added to MultiServer s appropriate internal list of data structures and displayed on the panel The user program receives data for geometric objects by sending a request message and then waiting for a message containing the data for that object GeoJAVASheet sends a message to its corresponding user program when the user presses the Return button When the user program has explictly requested an object for input and the user hits the Return button then the last object app
5. 0 GeoPause Please enter a simple polygon 23 P Graphic_Read GeoPause Please enter an interior point pti Graphic_Read final VISIBILITY amp P pt1 SetOutSheetColor next_color GeoPause Ready to see the visibility polygon final gt Graphic_Write Note that the call to IPCServiceSetup checks the arguments to the program and assumes that if there are arguments they are the host and port number for the GeoJAVASheet to which it should communicate This format should be followed especially if the user wishes to execute their program off the web server which will call the program with the host and port number as arguments Figure 12 displays the ChannelGuide when user Frank enters the system User Kiyoko is already on channel channell and Frank is about to join her At that time user Kiyoko sees what is in Figure 13 But when she sees Frank join the channel she can send him messages as in Figure 14 which is what Frank sees in his chat window When Kiyoko runs her algorithm notice that she does indeed have the floor both Kiyoko and Frank will see the same display on their sheets The reader may follow the program along with the following series of figures First in Figure 15 Kiyoko and Frank see the request to enter a polygon brought up because of the call to GeoPause in the program Next after Kiyoko has entered a polygon and hit the Return button she and Frank both get a view
6. 119 B V Smith The Xfig User Manual 1993 32 Appendix The following is the java source code for MultiServer Note that it works closely with Classes Connection and Vulture public class MultiServerTCP extends Thread Default port to listen on protected final static int DEFAULT_PORT 8411 protected final static int DEFAULT_PORT2 8511 private int port private ServerSocket listen_socket protected ThreadGroup threadgroup protected Vector connections protected Vulture vulture protected Vector ports new Vector protected Vector floorQ new Vector protected Vector channelQ new Vector private Vector channelGuideQ new Vector private Vector names new Vector private Vector channels new Vector public boolean locked false public static final int BUFSIZE 4096 public static final int MAXCHANNELS 10 also set in channelGuide protected String last_ss new String Exit with an error message when an exception occurs public static void fail Exception e String msg System err println msg e System exit 1 Create a ServerSocket to listen for connections on start the thread public MultiServerTCP int port boolean verbose Create our server thread with a name super Server if port 0 port this port port try listen_socket new ServerSocket port DEFAULT_PORT 33 N x Xx Xx Xx Xx Xx Xx x x catch
7. Windows b Chat box guest2 Connecting to server done quest2 enters the conversation Users on Selected Channel Java Applet Window Figure 4 Chat Box Applet 4 6 Compilation Tool The compilation tool allows user defined programs written in C C to be compiled and executed directly on the GeoJAVA server It is a series of common gateway interface CGI forms that upload the code create a corresponding Makefile for it compile it and if the compilation is successful execute it with the user s corresponding host and port number Unsuccessful compilations will result in a page listing the compilation errors so that the user may debug their own code and restart the process with the corrections With this tool users no longer need to worry about obtaining the appropriate libraries for their system installing and compiling them Of course security precautions must be 16 taken in order to ensure that the user s program does not contain any malicious code It is possible for users to include system code which may corrupt the system Therefore extra checks during the upload stage of the tool ensure that such malicious code is not used Records of those who have been using the compilation tool keep track of the users and their actions while still maintaining a certain level of privacy The following series of illustrations demonstrates the steps in the compilation process Figure 5 is the first page where t
8. beneficial because of the large size of the libraries used to implement geometric algorithms The effort required to download and install these libraries are oftentimes not worth it especially when the user only needs them for a single program or algorithm that he she would like to execute or implement The idea of a collaboratory is also to enable remote users with expertise in specific areas of a scientific field to collaborate with one another viewing the data that is pertinent to each user s specialty in order to come up with a solution to a particular problem For computational geometers or practitioners dealing with geometric data most everyone is interested in the execution and analysis of geometric algorithms so a collaboratory for geometric computing would provide remote users in a group with the facilities to view the execution of an algorithm implemented by any member in the group and to give feedback to one another regarding the algorithm In order to implement such a collaboratory distributed visualization of algorithms or at a bare minimum remote execution of algorithms needs to be supported Any user connected to a network should be able to have access to the collaboratory and immediately begin collaborating with other users currently connected to the collaboratory This implies that such a collaboratory must be independent of the users platform To implement a collab oratory from scratch that meets the requirement is by no mea
9. file has been spooled to disk as Amp geo 1 65 1 The file s reported name on the client machine is c demetep visib test_vistb c The file s reported Content type possibly none was application unknown content type c_auto_file The contents of tmp geo 165 1 are as follows include lt gecLEDA geo_polygon h gt include lt stdic h gt include lt stdlib h gt include lt string h gt include lt geoIPC port h gt include lt geoLEDA geo_plans h gt iuclude lt yeoLEDA yeo_polyyou h gt include lt geoLEDA geo_polyalg h gt int next_color static int ic 0 int ce switch ic case U c BLUE oreak case 1 c CREEN break case 2 c CYAN break case 3 c RED break case 4 c MAGENTA break default break ic 1c 1 8 5 Figure 6 Intermediate page 18 Compilation Page Netscape A A stop http geomamos cgi shl genmake pl Compilation Page compiling geo 252 1 geo 252 1 c In function int main int char geo 252 1 c 34 P undeclared first use this function geo 252 1 c 34 Each undeclared identifier is reported only once geo 252 1 34 for each function it appears in You will need to correct your source file and try again from here An Online Manual is also available Figure 7 Compilation output with error messages In addition a link for an online manual is available in case the user would like to consult documentation on the us
10. new String st nextToken if msg equals Xfloor request msg equals floor request if serv add2Q hoststr portstr channel out println floor granted else if msg equals Xfloor release msg equals floor release if serv remfromQ hoststr portstr channel out println floor released else out println MSPause only one else if msg startsWith Draw serv broadcastDraw msg substring 5 portnum GeoSheetStdOut 0 else if msg startsWith XDraw serv broadcastDraw msg substring 6 portnum GeoSheetStdOut 0 else reply to UP serv send2UP msg portnum serv_num else if line startsWith A connect st new StringTokenizer line substring 10 I serv_str new String st nextToken hoststr new String st nextToken UPport new Integer st nextToken intValue myType new String UP if serv GJSHasFloor hoststr UPport serv_str System out println serv_str UPport UPport else hoststr serv findFloorGJS hoststr UPport st new StringTokenizer hoststr hoststr st nextToken UPport new Integer st nextToken intValue else if line startsWith Aldisconn 46 try out close in close client close catch IOException e2 System out println Yow else if line startsWith B processUP line substring 2 else if line length gt 0 broadcast line catch IO
11. queue becomes the floor manager for the group Finally MultiServer also functions as the GeoManager of the system After the initial execution of an algorithm if the user modifies the original data input MultiServer will send messages to GeoJAVASheet to update the output dynamically This allows for true animation and easier debugging of algorithms for the developer Furthermore when users join a channel in the middle of the execution of an algorithm MultiServer allows these users to catch up on the algorithm execution Connection String channel String username int port_number String host name class The Connection object is responsible for receiving the messages sent by its cor responding GeoJAVASheet chat box or user program and then processing it appropriately Messages from GeoJAVASheets go through MultiServer to broadcast to the GeoJAVA Sheets of every member of its group or to send to their user program messages from chat boxes are broadcast directly to the chat boxes of every member of its group and the user program s messages are sent to the GeoJAVASheets in its channel Messages from GeoJAVASheets requesting for or releasing the floor are forwarded to MultiServer with its corresponding channel hostname and TCP port number Vulture class The Vulture class is a simple thread that informs MultiServer when a connection has been closed or lost and cleans up the lists Whenever possible the Connection object will no
12. triangulation program that A has executed Each student will be able to see the same set of points that A is sending to the program as input and the animated execution of the triangulation program on each of their browsers If students have questions or comments they may type them in the chat box and may also receive control of the floor upon release by A to input their own set of input points that is distributed to the rest of the group In doing collaborative research the current problem in the development of a new algo rithm is in explaining what the actual execution looks like to remote parties Up to now researchers have been using e mails or transferring files of their algorithms describing ver bally what each step of the execution is on a frame by frame basis The GeoJAVA system provides a solution to this problem For instance a group may consist of several researchers located at different sites One of the researchers say B may have developed a new algo rithm to solve a specific problem for which she would like advice from the others So upon receiving control of the floor B may execute her algorithm to present to the others Any of the other researchers may then receive the floor to give advice or make improvements on the algorithm The changes to the code may be made by B the code recompiled and then immediately re executed for the others to see Verbal communication is all performed through the chat box Thr
13. 1 added by BJM username line substring i 11 added by BJM myType new String CHAT else channel line substring 8 if hoststr null serv addChannel hoststr portnum channel else if line startsWith channelGuide request added by BJM Vector CHG serv getCGQ String outline new String CHG for Enumeration enum CHG elements enum hasMoreElements outline outline concat new String enum nextElement out println outline else if line startsWith Can I Connect line line substring 15 while serv locked int response serv canIConnect line if response 1 int i line index0f added by BJM channel line substring 0 i added by BJM oldChannel channel added by BJM username line substring i 1 added by BJM out println Connection Request response else if line startsWith HOST st new StringTokenizer line substring 4 hoststr st nextToken portstr st nextToken portint new Integer portstr portnum portint intValue 45 myType new String GJS isGJS true else if line startsWith CLOSE portstr line substring 6 serv removeChanne hoststr portnum channel serv remfromQ hoststr portstr channel else if line startsWith GJS st new StringTokenizer line substring 4 serv_num new Integer st nextToken intValue portstr st nextToken msg
14. CP socket is created on the server and the applet communicates di rectly to that port Therefore using TCP sockets applets can be easily created that provide distributed geometric computing In addition to the language limitations TCP is favorable because of its stability especially in large networks UDP packets are not acknowledged by the recipient so the farther the distance between the sender and receiver the more prone the packet is to get lost This often results in the user s algorithm hanging during execution without any method of recovering itself The user is unfortunately forced to kill the execution of the algorithm in this case Adding error checking packets for acknowledgements would most likely only increase the number of lost packets over the network We create a GeoLIB library that supports TCP messaging Since setup and disconnect packets are not used for each message sent it is only required upon connection disconnection to from the system the packet sizes are smaller and TCP s reliability prevents the transmission speed from getting degraded as much compared to the UDP transmission protocol 3 Related Work As is evident at the Computational Geometry Interactive Software page http www cs duke edu jeffe compgeom demos html many geometric algorithm visual ization tools have been implemented and the Complete Collection of Algorithm Anima tions at http www cs hope edu alganim ccaa ge
15. Exception e When we re done for whatever reason be sure to close the socket and to notify the Vulture object Note that we have to use synchronized first to lock the vulture object before we can call notify for it Note running asynchronously now finally try out close in close client close catch IOException e2 System out println Yow channel Kill me please handle user program message public void processUP String line serv broadcastDraw line UPport serv_str 1 public void send String msg if out checkError this channel Kill me please else out println msg Here we send a message to everyone who is on the channel public void broadcast String msg Connection you String toName StringTokenizer st 47 st new StringTokenizer msg st nextToken st nextToken toName st nextToken if toName equals Enumeration e serv connections elements while e hasMoreElements you Connection e nextElement if you channel equals channel you send msg else Enumeration e serv connections elements while e hasMoreElements you Connection e nextElement if you channel equals channel amp amp you username equals toName you send msg This class waits to be notified that a thread is dying exiting and then cleans up the list of threads and the graphical list class Vulture extends Th
16. IOException e fail e Exception creating server socket Create a threadgroup for our connections threadgroup new ThreadGroup Server Connections Initialize a vector to store our connections in connections new Vector Create a Vulture thread to wait for other threads to die It starts itself automatically vulture new Vulture this Tell the world we are running if verbose System out println Multiserver is running Start the server listening for connections this start The body of the server thread Loop forever listening for and accepting connections from clients For each connection create a Connection object to handle communication through the new Socket When we create a new connection add it to the Vector of connections Note that we are running asynchronously We used to use synchronized to lock the Vector of connections The Vulture class does the same so the vulture won t be removing dead connections while we re adding fresh ones This version seems more resistant to deadlock public void run try while true Socket client_socket listen_socket accept System out println socket accepted client_socket getPort Connection c new Connection this client_socket threadgroup 3 vulture connections addElement c catch IOException e fail e Exception while listening for connections 34 Start the server up listening on an
17. Towards Web Based Computing Kiyoko F Aoki and D T Lee Department of Electrical and Computer Engineering Northwestern University Evanston Illinois 60208 U S A Email dtlee kaoki ece nwu edu Abstract In a problem solving environment for geometric computing a graphical user interface or GUI for visualization has become an essential component for geometric software develop ment In this paper we describe a visualization system called GeoJAVA with a GUI which enables the user or algorithm designer to execute and visualize an existing code in the li brary or develop a new code over the internet The library consists of geometric code written in C C The GUI is written using Java programming language Taking advantage of the socket classes and system independent application programming interfaces API s that come with the Java language GeoJAVA provides a platform independent environment for distributed geometric computing Users are able to remotely join a channel or discussion group in a location transparent manner to do collaborative research Then the visualization of an algorithm a C C program located locally or remotely and controlled by a floor manager can be viewed by all the members in the channel through a visualization sheet called GeoJAVASheet The execution of the algorithm can then be re run dynamically to demonstrate the changes in the output upon modification of the input data by the floor manager A ch
18. age of the functions in the GeoLIB library If the compilation is successful a form for the host and port number will be given as in Figure 8 When the user enters the appropriate data and clicks the Submit button the algorithm will execute and the output be displayed on the specified GeoJAVA Sheet and other GeoJAVASheets in the same channel The completion of the execution of the algorithm will produce a page like Figure 9 At this point the user may submit their code to add to the Algorithm Browser which is shown in Figure 10 The Algorithm Browser lists the available algorithms for execution Anyone with the floor may bring up this page and sample any of the algorithms given The next section gives a general description of the architectural design of the GeoJAVA system followed by an example of a user s code and its execution 19 Compilation Page compiling geo 165 l c NOW LINKING COMPILATION SUCCESSFUL To execute your algorithm bring up GeoJAVASheet enter the host and port number below and click the Submit button to execute I Enter host name Enter port number _ E Figure 8 Compilation output Algorithm Execution Completed Successfully Netscape STO p http geomamos cgi shl compile simple form p M Algorithm Execution Completed Successfully If you would like to post your program to the Algorithm Browser click here Figure 9 Algorithm Execution Compl
19. as in Figure 16 requesting a point Notice the polygon displayed on the sheet As soon as Kiyoko hits the Return button the polygon is displayed on all of the other users GeoJAVASheets on the channel In this case only Frank sees the polygon entered Figure 17 displays the change in the GeoJAVAPause window to prepare the user for the output and Figure 18 is the final output to the program Figure 19 displays another example of three GeoJAVASheets and three chat boxes con nected to the same channel while running on three different hosts 24 S Channel Guide channel Figure 12 ChannelGuide 25 Ea GeoJAVASheet 10 Northwestern University Flectrical and Computer Engineering Di lolx HOST geomamos PORT 1151 Return Undo Delete 0FF Modiy OFF Move OFF Delete All Qui Toggle Grd i l il il No datatype x X FG Ye PE H You have he floor Line Atributes Black DI fi gt Text Atributes courer 7 fre si Line Style Soio gt Fill Style None aaa ARIE Send a message Connecting to server done kiyoko enters the conversation x kiyok Users on Selected Channel ae 210 ava Apple Window Figure 13 Kiyoko s View 26 Chat box Frank Sond a mag TM Connecting to server done Frank enters the conversation kiyoko says Hi Frank Figure 15 Enter a polygon request 27 Ea GeoJAVASheet 1 0 Northwestern University E
20. at box is also provided for verbal communication among all the members Furthermore this system not only allows visualization of pre compiled geometric codes but also serves as a web based programming environment where users may submit their own geometric code compile it with the visualization libraries provided by the system and visualize these directly over the web sharing it with other users immediately Supported in part by the Office of Naval Research under the Grants No N00014 95 1 1007 and No N00014 97 1 0514 A preliminary result was presented at the Workshop on Geometric Software held in INRIA Sophia Antipolis France in June 1997 1 Introduction As the computer and communication technology advances communication via e mails or World Wide Web has become commonplace in our daily activities In the computing world collaboration via Internet has gained popularity recently The notion of a collaboratory is introduced in a report on Distributed Collaboratory Experiment Environment 8 which refers to an integrated tool oriented computing and communication system that supports scientific collaboration In other words it is a computing system that allows remote parties to gain access to scientific resources such as expensive and physically large equipment that would otherwise not be accessible As in any other scientific computing disciplines the area of geometric computing would find such a collaborative system
21. d a priority super threadgroup connection_number this setPriority priority Save our other arguments away client client_socket this vulture vulture serv theserver channel The Default Channel oldChannel The Default Channel username UnKnown Create the streams 43 try in new DataInputStream client getInputStream out new PrintStream client getOutputStream true catch IOException e try out close in close client close catch IOException e2 System err println Exception while getting socket streams e return And start the thread up this start public void sendUpdate Vector CHG serv getCGQ String outline new String CHG for Enumeration enum CHG elements enum hasMoreElements outline outline concat new String enum nextElement out println outline System out println here s the data outline public void run String line Integer portint StringTokenizer st String msg Send a welcome message to the client send 0 WELCOME super getName try for Gis 4 yield try sleep 500 catch InterruptedException e line in readLine if line null break line line trim 44 if line startsWith CHANNEL if isGJS int i line index0f added by BJM channel line substring 8 i 1 added by BJM oldChannel line substring 8 i
22. e reliable We briefly describe the main functions from the GeoLIB library that the programs use in order to visualize algorithms next IPCServiceSetup IPCServiceSetup char host int portnum This function sets up the initial TCP connection between the user program and GeoJAVASheet It can have no arguments in which case the user will be prompted for the host and port number at the command line or it can take the host and port number for an input and output GeoJAVASheet that has the floor It then establishes a socket connection between itself and MultiServer with a Connection object serving as an interface Any messages sent to MultiServer contain the GeoJAVASheet ID to which it corresponds so that MultiServer can forward them to the appropriate GeoJAVASheet The user program must begin with the IPCServiceSetup function before any visualization functions are called Graphic_Read and Graphic_Write initiated from user program The Graphic_Read and Graphic_Write visualization functions are member functions imple mented in every geometric object and are issued from the user program Graphic_Read will cause GeoJAVASheet to return to the program the last object input onto the sheet The process is as follows 1 Graphic_Read requested from user program set choice box on GeoJAVA Sheet to the requested object type 2 user inputs the object onto the sheet 3 user presses the Return button located at the top of GeoJAVASheet which 4 se
23. ed KFA 1 16 98 for multiple channels Enumeration f floorQ elements while f hasMoreElements String s String f nextElement if s endsWith chanName success false if success true return Success public boolean hasMore String chanName Object 0 Enumeration e floorQ elements o e nextElement while e hasMoreElements if String o endsWith chanName return true return false public boolean remfromQ String hoststr String portstr String chanName String request byte barray new byte BUFSIZE 36 InetAddress address boolean success Enumeration e String newHost new String String newPort new String String newSS new String int portno newport 1 if floorQ contains hoststr portstr chanName if hasMore chanName floorQ removeElement hoststr portstr chanName e floorQ elements Object o e nextElement while String o endsWith chanName o e nextElement StringTokenizer st new StringTokenizer String o newHost st nextToken newPort st nextToken request new String floor granted Connection you e connections elements portno new Integer portstr intValue while e hasMoreElements you Connection e nextElement if you myType equals GJS amp amp you channel equals chanName amp amp you hoststr equals newHost amp amp you po
24. el returns 1 if there are already MAXCHANNELS channels returns 2 if it is an invalid username public int canIConnect String req locked true int i req index0f String C req substring 0 i String N req substring i 1 System out println C C N N String c C toLowerCase String n N toLowerCase if names contains n n equals locked false return 2 if channels size gt MAXCHANNELS locked false return 1 else add2CGQ C N locked false return 0 42 This class is the thread that handles all communication with a client It also notifies the Vulture when the connection is dropped class Connection extends Thread static int connection_number 0 protected Socket client protected Vulture vulture protected DataInputStream in public PrintStream out protected MultiServerTCP serv public String channel new String public String oldChannel new String public String username public String myType new String public String portstr new String public int portnum public String hoststr new String public int UPport 1 public boolean isGJS false public String serv_str new String public int serv_num Initialize the streams and start the thread public Connection MultiServerTCP theserver Socket client_socket ThreadGroup threadgroup int priority Vulture vulture Give the thread a group a name an
25. ended to the panel corresponding to that displayed in the choice box which has been updated with the object requested from the user program will be stored in a message to be sent to MultiServer The user program s ID is stored in GeoJAVA Sheet upon the program s initialization and thus has been stored in this message as well Once MultiServer receives this message it forwards it to the appropriate user program There is an additional feature in the application version of GeoJAVASheet where the data on the sheet may be saved to and opened from files Two additional Open File and Save buttons provide this option The data is stored in XFig format 14 just as in GeoMAMOS but other formats will be supported in future versions Figure 3 is an instance of the GeoJAVASheet application running under Windows 4 4 GeoLIB Geometric Library The GeoLIB library in the current version consists of two parts the LEDA 12 and Ge oLEDA libraries Both libraries are written in C C An advantage of this is that users who have developed algorithms written in C C prior may continue to use their algorithms 13 STATA VASheet 1 0 Northwestern University Electrical and Computer Engineering Department l FA HOST geomamos PORT 1620 _Retum Undo Delete OFF Modify OFF Move OFF Delete All _Quit Toggle Grid Open File Save x 4 Y 326 Z 0 Request Floor You do not have the floor X 4 Line Attributes Black z
26. eoSheet is the 2 D GUI for GeoMAMOS that is the interface with which users interact to communicate with their algorithms GeoManager provides the dynamic manipulation of algorithms by allowing users to execute their program then modify the original input data and simultaneously see the changes in the algorithm s output A drawback of GeoMAMOS is that it was written in C C for the X Windows environment running Unix so users who do not have access to such machines installed with the GeoMAMOS software are not able to make use of the visualization tool In view of the above a system independent version has been implemented in the form of the GeoJAVA system The following section will describe the design of the GeoJAVA system which allows visualization of users algorithms written in C C in a distributed fashion Groups or channels are formed by simply specifying a common channel name when entering the system and distributed visualization process can begin immediately upon execution of a program by the floor manager 4 Design Description The GeoJAVA system consists of six major components 1 MultiServer 2 ChannelGuide 3 GeoJAVASheet 4 GeoLIB 5 Chat box and 6 a compilation tool The design of each of these components will be described next 4 1 MultiServer MultiServer is a Java application adapted from the Free Internet Conferencing Tools FICT home page at http www sneaker org fict Slight modifications were inco
27. er for compilation and may complement the GeoMAMOS system It is our hope that with this visualization prototype a foundation can be established on 30 top of which a problem solving environment for geometric computing and other fields of scientific research and development can be built 8 Acknowledgements We would like to thank the following people for their help in the initial implementation of GeoJAVASheet Mehmet Sayal Lisa Singh Takashi Yoshikawa We would also like to acknowledge Benjamin McLean for his implementation of ChannelGuide and file I O on the application version of GeoJAVASheet and Steve Loranz and Matt Firlik for their help with the compilation tool References 1 K Aoki The Prototyping of GeoManager A Geometric Algorithm Manipulation Sys tem Master s Thesis December 1995 2 J E Baker I F Cruz L D Lejter G Liotta and R Tamassia Mocha http loki cs brown edu 8080 papers MochaFS html 3 L Beca G Cheng G C Fox T Jurga K Olszewski M Podgorny P Sokolowski K Walczak Web Technologies for Collaborative Visualization and Simulation NPAC Technical Report SCCS 786 Syracuse University NPAC Syracuse NY submitted Jan uary 6 1997 4 M H Brown M A Najork R Raisamo A Java Based Implementation of Collabora tive Active Textbooks in 1997 IEEE Symposium on Visual Languages pages 372 379 IEEE Computer Society September 1997 5 M H B
28. etion 20 Welcome to GeoJAVASheet Netscape Stop GP http geomamos geojava applet browser html 2 GeoJAVA Algorithm Browser Enter host name Enter port number Select an algorithm Constrained Delaunay Triangulation Triangulation and 3 coloring Visibility Algorithm Press _Execute to run the algorithm ie Figure 10 Algorithm Browser 21 res sssseio lesse alc a eee a an ad GeoJAVASheet a Ta og i I Connection User 1 s algorithm splay I Chat Box Connection User 1 Connection l Connection i GeoJAVASheet Chat Box User 2 Figure 11 GeoJAVA System Architecture 5 Architectural Design Combining the components described in the previous section the result is a complete system as illustrated in Figure 11 The figure is an instance of the system where User 1 and User 2 are on the same channel User 1 has the floor and is executing an algorithm The dotted area containing MultiServer is the Java application that runs on the web server at a specified TCP port When a new user enters a new Connection instance is created for the user s GeoJAVASheet chat box and possibly user program Note that the Connection objects are clients that MultiServer instantiates when the users enter the system and these Connection objects communicate to their counterpart applets thro
29. eturn true return false public String findFloorGJS String hoststr int UPport String chanName new String Connection you StringTokenizer st String newHost String newUP 40 Enumeration c connections elements while c hasMoreElements you Connection c nextElement if you myType equals GJS amp amp you portnum UPport amp amp you hoststr equals hoststr chanName you channel break c floorQ elements while c hasMoreElements Object o c nextElement if String o endsWith chanName return String o chanName new String hoststr UPport return chanName changed by BJM public void add2CGQ String newchannel String newuser Enumeration e connections elements Connection you channelGuideQ addElement new String newchannel newuser channels addFElement newchannel toLowerCase names addElement newuser toLowerCase while e hasMoreElements you Connection e nextElement you sendUpdate public void someoneDied String chan String nam 41 channelGuideQ removeElement new String chan nam names removeElement nam toLowerCase channels removeElement chan toLowerCase public Vector getCGQ return channelGuideQ this method checks the names and channels vectors to see if a user can add with the given name and channel Returns 0 if the user can connect on that chann
30. gram and Delaunay triangulation of the user s input while points are added or moved It illus trates incremental construction of the Delaunay triangulation and includes a recorded demo ModeMap by David Watson http www iinet com au watson modemap html Modemap is an applet that draws Voronoi diagrams Delaunay triangulations natural neighbor circles and radial density contours on a sphere This is a single 3D applet whose only purpose is to illustrate the relationship between these geometric concepts on a sphere It also allows for moving of points The Geometry Applet by David Joyce http alephO clarku edu djoyce java Geometry Geometry html The Geometry applet illustrates Euclid s Elements It lets users set up simple geometric objects in 3D as well as constraints through the use of Java parameters and then displays the effects as objects are moved Alpha shape demo from NCSA which requires VRML http fiaker ncsa uiuc edu alpha demo html This alpha shape demo is an online Alvis demo that serves as a web based interface to Alvis software It is used to clarify concepts of Alpha Shapes and Alpha Ranks Three data sets are available Please refer to http fiaker ncsa uiuc edu alpha reference html for references regarding Alpha Shapes Ranks Although these applets are successful in demonstrating various computational geometry algorithms if a researcher say wanted to test and develop their own algorithm they
31. he file is uploaded from the user s local disk to the server File Upload Form Netscape an lew GO communcser Hep File Upload Form This page allows you to upload a file Note that the script will limit the size of the file to around 500k so that the server doesn t get swamped with data Please fill in the file upload form below Press to upload the file Figure 5 Code upload page The user may specify a note for their code normally the name of the algorithm During the upload the CGI script checks the filename for special characters and also parses the code for any malicious code such as system calls Upon completion of the upload the contents are displayed to ensure that the correct file has been uploaded completely along with the user s notes as in Figure 6 A link for a script that performs the actual compilation is also given The compilation will then take place after which the output of the compilation will be displayed If it is unsuccessful a page such as in Figure 7 will be displayed allowing the user to see the compilation errors In this case a link back to the first file upload page is given but the user may also use the Back button on their browser to return to the first page 17 File Upload Results Netscape File Upload Results You ve uploaded a file Your notes on the file were visibility algorithm Proceed to the compile page to begin compilation The
32. lectrical and Computer Engineering D Ei GeoJAVAPause Please enter an interior point Figure 16 Enter a point request Ea GeoJAVASheet 1 0 Northwestern University Electrical and Computer Engineering D zaj GeoJAVAPause Ready to see the visible region Figure 17 Ready request 28 Ea GeoJAVASheet 1 0 Northwestern University Electrical and Computer Engineering D _ Rai fue Ble soia None Figure 18 Final program output onnecting to server done alfred enters the conversation om enters the conversation enjamin enters the conversation Send a message i onnecting to server done om enters the conversation benjamin enters the conversatio Figure 19 GeoJAVA System Demo 29 7 Conclusion and Future Work The GeoJAVA system provides a comprehensive set of tools with which any user on the World Wide Web can learn and implement concepts of computational geometry as well as collaborate with remote users on algorithm design This is provided in a distributed and location transparent manner System independence and modular implementation also makes the system scalable and the dynamic manipulation of geometric algorithms and the online compilation tool are unique features that make the GeoJAVA system useful for computational geometers and students Using this GeoJAVA system as a stepping stone many other valuable systems may be developed For example Sun Microsystems has recently an
33. ly we discuss our plans for future work 2 Java Programming Language The Java programming language by Sun Microsystems provides two major features that make it very applicable to distributed geometric computing They are sockets and GUI objects By simply declaring a new ServerSocket data object in a server application client applications can begin communicating to it by using a Socket class declared similarly without worrying about the type of system on which the applet or application may be running GUI objects such as buttons canvases and panels can also be created easily with predefined classes provided by the Java library Both datagram User Datagram Protocol or UDP and stream based Transmission Con trol Protocol or TCP sockets are provided in the Java application programming interface API However security issues prevent applets from waywardly creating sockets on users machines sockets can only be created on the host that provided the applet Therefore if a Java application is running on the server another applet cannot create a socket on the remote host to even connect back to the server application Datagram sockets require such a configuration Although Java applications as opposed to applets would work without a problem that would defeat the purpose of allowing users to easily access the system without having to download the application itself Stream based sockets however can be used in an applet where the T
34. nds the data for the object to MultiServer which forwards it to the user program In Graphic_Write the opposite action is performed The user program sends object data to GeoJAVASheet through MultiServer and GeoJAVASheet displays the object The process is as follows 1 Graphic_Write command sent to GeoJAVASheet with the object s data 2 the object is added to the corresponding list of geometric objects and 3 Geo JAVASheet displays the object Using these libraries a user may develop geometric algorithms that can perform any geometric computing they would like without concern for implementing the display of in termediate or final results in their code 15 4 5 Chat Box The Chat Box is another applet adopted from the Free Internet Conferencing Tools web page and is a simple GUI consisting of a text field in which to enter text and a textbox in which all messages from users within the same channel are displayed In addition it lists the users currently in their channel It maintains a PrintStream object that handles the displaying of all of the messages a DatalnputStream that receives the messages and a Socket class with which the connection to MultiServer is made A user may select a specific username on the userlist in order to send messages to users privately or messages may be broadcast to everyone on the channel by selecting the asterisk also on the list Figure 4 is an instance of the Chat Box running under X
35. nounced its 3D API A great contribution to computational geometry can be made with the implementation of a GeoJAVA system that visualizes 3D geometric algorithms Also MultiServer may become a bottleneck as more and more users and groups participate in collaborations Therefore a proposed workaround is to create a new MultiServer instance every time a new group is formed The check for duplicate group names may be performed by communication among the existing MultiServer instances This would make the GeoJAVA system more scalable Furthermore a Java version may be developed of the GeoLIB library which may eliminate the need for a large C C library for those who do not know or do not wish to implement their algorithms in C C In the current version of GeoJAVASheet the JDK version 1 0 2 has been used since JDK 1 1 has yet to be implemented in most of the browsers in use today However once its stability and popularity have become the norm we plan on upgrading GeoJAVASheet to at least JDK 1 1 The need for compilation is expected to remain however so the compilation page may be improved or expanded In order for users to retrieve their compiled code an additional tool may be developed which can be downloaded to the user s machine This tool would connect over the Internet to the appropriate server containing the libraries for the user s system and then compile the code on the local machine itself This would eliminate the need to use a brows
36. ns obvious especially when visualization or graphics output is involved for which all sorts of display devices have to be supported However since Internet and web browsers on the World Wide Web are readily accessible by many researchers on the network building a collaboratory on the web seems to be a plausible solution The Java programing language developed by Sun Microsystems which is considered platform independent is a natural choice of language to use to implement such a collaboratory Thus came the development of the GeoJAVA system a Web based in teractive visualization system that provides 1 a Java based GUI graphical user interface called GeoJAVASheet 2 a Java based chat box that allows users in separate groups to communicate verbally 3 a library of geometric algorithms called GeoLIB 4 a compilation tool allowing users to implement user defined algorithms using the GeoLIB library and 5 distributed visualization of geometric algorithms There are many applications of this system Among them are distance learning and collaborative research on geometric computing For example a classroom can be formed by a group in which the teacher of a geometric code say A initially has control of the floor That is A is the user interacting directly with the code and the rest of the users in the group become students Each student in the group can then watch the execution of the same code say a Delaunay
37. od Invocation RMI technology allows applets on different machines to communicate with each other with the views of an algorithm located on different machines Although JCAT runs on all Java enabled browsers at the time of this writing only HotJava 1 0 can support the collaborative features because it requires JDK 1 1 The algorithms that are visualized are written in Java and are based on BALSA s notion of interesting events to communicate the operations of the algorithm to the views 5 and group communication is implemented by having each student specify the name of the teacher s machine where the algorithm is running The focus of Tango is different from that of the GeoJAVA system in that it is geared towards medical and scientific researchers It is very useful in an environment where collab oration is needed from different people with completely different specialties For example a consultation for a certain surgical procedure may require the expertise of a neurologist cardiovascular specialist and a physical therapist where all three need different views of the same data Technically speaking the full fledged Tango requires the installation of a plug in for the browser and only works with Netscape 3 0 whereas the GeoJAVA system is java pure and so any browser can be used to access it Promondia s focus is also different in that it attempts to give users a foundation for real time communication using Ja
38. ometric html gives a comprehensive list of geometric algorithms written in Java These applets demonstrate Java s write once run everywhere concept 7 Once a user implements her Java applet that demonstrates an algorithm any user with a Java enabled browser can execute it The following is a listing of a few notable java applets from these lists GeomNet at the Center for Geometric Computing at Johns Hopkins University http www cge cs jhu edu geomNet GeomNet is a system for performing distributed geometric computing over the Inter net It provides a list of GeomNet supported algorithms from which a single user can choose an algorithm they would like to execute Geometric computing is distributed in that the algorithms are available for anyone on the Internet who would like to see the execution of an algorithm However it is not implemented for groups of users to simultaneously see the execution of a single algorithm One of the components of GeomNet is Mocha 2 at the Center for Geometric Computing at Brown University http loki cs brown edu 8080 pages Mocha html Mocha is a Java applet that com municates with an algorithm server which allows users to select geometric algorithms for which they can provide input VoroGlide by Christian Icking Rolf Klein Peter Kollner and Lihong Ma http wwwpi6 fernuni hagen de java anja index html en VoroGlide is an applet that smoothly maintains the convex hull Voronoi dia
39. oneDied c oldChannel c username added by BJM c null else if c isAlive server remfromQ c hoststr c portstr c oldChannel added by KFA server connections removeElement c server someoneDied c oldChannel c username added by BJM c broadcast 0 OBITUARY c getName c null 49
40. optionally specified port public static void main String args int port 0 boolean verbose false if args length 0 new MultiServerTCP port verbose else if args length 1 if args 0 equals v verbose true new MultiServerTCP port verbose else try port Integer parseInt args 0 catch NumberFormatException e port 0 new MultiServerTCP port verbose else if args length 2 amp amp args 0 equals v try port Integer parseInt args 1 catch NumberFormatException e port 0 verbose true new MultiServerTCP port verbose else System out println Usage java MultiServerTCP v lt port gt public void removeChannel String hoststr int portnum String chanName floorQ removeElement hoststr portnum chanName channelQ removeElement chanName hoststr portnum Enumeration e channelQ elements while e hasMoreElements Object o e nextElement System out println o0 e floorQ elements while e hasMoreElements Object o e nextElement System out println 0 35 public boolean add2Q String hoststr String portstr String chanName String request Integer portint int portnumber bytecount 0 byte barray new byte BUFSIZE InetAddress address boolean success success true if floorQ isEmpty floorQ addElement hoststr portstr chanName success true else Modifi
41. ough these examples one can see the benefits of visualization the phrase a picture is worth more than a thousand words indeed rings true However not only can the GeoJAVA system visualize static data but it can also serve as an interactive visualization system Users may manipulate the visualized data and simultaneously see the change in the algorithm s output This feature applies to programs that are in the library or are user defined and runs on top of a distributed environment which makes the GeoJAVA system a powerful tool with different utilities Returning to the first example then after the Delaunay triangulation has been executed user A may demonstrate how the triangulation changes when a specific point is moved to a different location by simply selecting a point and moving it across the sheet The GeoJAVA system automatically handles the dynamic re execution of the algorithm and updating of the sheets in the group As technology advances and becomes more readily available audio and video communi cation can easily be added to the system for a greater collaboratory feel This is due to the modularity of each component of the system which will be described in detail in the following sections In the next section we briefly introduce features of the Java programming language pertinent to the GeoJAVA system This will be followed by a review of related work then a description of the design of the GeoJAVA system and final
42. read protected MultiServerTCP server protected Vulture MultiServerTCP s super s threadgroup Connection Vulture Server S setPriority 5 this start This is the method that waits for notification of exiting threads and cleans up the lists It is a synchronized method so it acquires a lock on the this object before running This is necessary so that it can call wait on this Even if the the Connection objects never call notify this method wakes up every five seconds and checks all the connections just in case 48 Note also that all access to the Vector of connections and to the GUI List component are within a synchronized block as well This prevents the Server class from adding a new conection while we re removing an old one public synchronized void run Connection cC for try sleep 10000 catch InterruptedException e System gc Do we run into trouble here if not synchronized Assuming that something changes during the enumeration Enumeration e server connections elements while e hasMoreElements c Connection e nextElement if the connection thread isn t alive anymore remove it from the Vector and List And inform the deceased s friends if c channel equals Kill me please server remfromQ c hoststr c portstr c oldChannel added by KFA c stop server connections removeElement c server some
43. rown R Sedgewick A System for Algorithm Animation Computer Graphics 18 3 177 186 July 1984 6 U Gall F J Hauck Promondia A Java Based Framework for Real Time Group Communication in the Web Sixth International World Wide Web Conference 1996 31 7 8 10 11 12 13 14 J Gosling B Joy and G Steele The Java Language Specification Addison Wesley Developers Press Sunsoft Java Series 1996 W E Johnston and S Sachs Distributed Collaboratory Experiment Environments DCEE Program Overview and Final Report Lawrence Berkeley National Labora tory February 1997 D T Lee Visibility of a Simple Polygon Computer Vision Graphics and Image Processing 22 1983 207 221 D T Lee C F Shen and S M Sheu GeoSheet A Distributed Visualization Tool for Geometric Algorithms Intl J Computational Geometry Applications 8 2 April 1998 to appear S Naher LEDA A Library of Efficient Data Types and Algorithms Max Planck institut fiir informatik Technical Report A 04 89 Universitat des Saarlandes Saarbricken 1989 S Naher LEDA3 0 User Manual technischer Bericht A Fachbereich Informatik Universitat des Saarlandes Saarbriicken 1992 M H Overmars Designing the Computational Geometry Algorithms Library CGAL In Proceedings Workshop on Applied Computational Geometry May 27 28 1996 Philadelphia Pennsylvania pp 113
44. rporated for it to provide the services for the collaboration management of the GeoJAVA system It keeps track of the groups and the floor queue using the Connection and Vulture classes and also provides the dynamic manipulation of geometric algorithms MultiServer int port boolean verbose The MultiServer class is a separate Java program running on the web server which creates the server thread and establishes the socket at the port number specified by the DEFAULT_PORT global constant It then listens for connections from users Whenever a new connection is made a new Connection class is created and appended to the MultiServer s queue of connections A new Vulture object is also created which ensures that all of the connections are valid Each of these components will be described later Note that because all new users connect through MultiServer groups of users need not be concerned with the actual location of a server host Thus location transparency is supported MultiServer handles the floor control for each group by maintaining a FIFO queue When a new group is created the floor queue for this group is empty The first user to press the Floor Request button is added to the queue and becomes the floor manager Other users in the group who press this button thereafter are appended to the queue When the floor manager presses the Floor Release button he she is then removed from the queue and the successive user in the
45. rtstr equals newPort you send request newport you portnum if you serv_str equals newss you serv_str 37 adjust UP which originally connected with a different GeoSheet that had the floor e connections elements while e hasMoreElements you Connection e nextElement if you myType equals UP amp amp you UPport portno you UPport newport you hoststr newHost System out println Adjusted UP with you serv_str success true else success false System out println Floor Q now has e floorQ elements while e hasMoreElements Object o e nextElement System out println o return success public void broadcastDraw String msg int UPport String last_serv_str int sendUP StringTokenizer stringT request String mychann mess String hoststr Integer portInt int portnum int bytecount 0 byte barray new byte BUFSIZE InetAddress address Connection you 38 last_ss new String last_serv_str Enumeration e channelQ elements while e hasMoreElements String channstr String e nextElement stringT new StringTokenizer channstr mychann stringT nextToken hoststr stringT nextToken portnum new Integer stringT nextToken intValue if portnum UPport System out println UP found portnum find connections with same channel Enumeration c connections elements while c hasMoreElements
46. tify the Vulture thread when a connection is closed But even if the Connection objects never notify the Vulture this method wakes up every five seconds and checks all connections in case a Connection unexpectedly crashes before it is able to send a close 10 message The Java source code for these three classes are given in the Appendix 4 2 ChannelGuide ChannelGuide is an applet that ensures that multiple users do not enter the system with the same username This is the applet that the user first sees when entering the GeoJAVA system ChannelGuide takes the user and channel names requested by the user communicates with MultiServer to check the current user lists for duplicates and responds with the appropriate information either allowing the user to start up GeoJAVASheet or prompting for a different user name The ChannelGuide applet running on an X Windows system is shown in Figure 1 e Channel Guide Channels test Users on Selected Channel e ter Channel on which to Connect Enter your username E Enter Java Applet Window Figure 1 ChannelGuide Applet ChannelGuide functions by first communicating with MultiServer requesting the lists of channels and users currently on the system Once these lists are received it processes them to display If a used username is entered then a message is displayed indicating that the entered name is invalid Otherwise the ChannelGuide window disappears and a
47. ugh a TCP socket This architecture is an expansion of the AnnoyingChat MultiServer applets on the FICT home page 22 6 Example The user s program is written in C and has only a few simple rules for its structure to follow in order to work with the GeoJAVA system These rules consist of including the appropriate include files and calling IPCServiceSetup at the beginning of the program Then the code may make calls to Graphic_Read and Graphic_Write for the geometric objects used Details of these functions are given in Section 4 4 The following is an excerpt of a geometric algorithm that computes the visibility polygon from a point interior to a given simple polygon both the simple polygon and the source point are entered by the user from the GeoJavaSheet VISIBILITY is a function based on the algorithm by Lee 9 that takes as input a simple polygon and a point and produces as output the visibility polygon More details of this implementation can be found in Aoki 1 Header files include lt stdio h gt include lt stdlib h gt include lt string h gt include lt geoIPC port h gt include lt geoLEDA geo_plane h gt include lt geoLEDA geo_polygon h gt include lt geoLEDA geo_polyalg h gt main int argc char argv geopolygon P final GeoPoint pt1 node v final new geopolygon if argc gt 1 IPCServiceSetup argv 1 atoi argv 2 else IPCServiceSetup SetOutSheetFillStyle
48. va as opposed to having any distributed application based purpose Their focus is on satisfying the increasing demand for other network ser vices such as real time data feeds group communication and teleconferencing refer to http www6 nttlabs com papers PAPER100 PAPER100 java html for an online version of their paper Habanero uses Java applications as opposed to applets which means it is not necessarily web based Its components need to be downloaded and only Java components can be used for collaboration Thus Habanero has a limited scope The main difference between JCAT and the GeoJAVA system would be location indepen dence Whereas GeoJAVA system users may access the system through a single page and form a group using a single channel name JCAT requires channels to be formed by forcing students to specify the hostname of the teacher s machine This requires knowledge of who the the floor manager is beforehand That is only the teacher has control of the algorithm and the students may not request control of the floor Also the algorithm being displayed must be written in Java Therefore current algorithms written in C must be re written in Java in order for it to be useful under JCAT The GeoJAVA system is based on GeoMAMOS http www ece nwu edu theory geo mamos html part of which are GeoSheet 10 and GeoManager 1 which provide distributed visualization of geometric algorithms over a UNIX based network G
49. would not be able to make any practical use of these applets let alone demonstrate the same execu tion of their algorithm simultaneously on remote parties machines This lack of interactivity and customizability motivates the development of the GeoJAVA system Other Java based collaborative systems also worth noting are Tango 3 Promondia 6 and NCSA s Habanero Tango is a Java based system that allows remote users to collab orate over the Web Users with applications that they would like to make distributed may incorporate Tango s API into their code which would allow their application to commu nicate to a central server that handles the distribution of the application It provides nice multimedia features and is geared towards medical and scientific research Promon dia is a system that provides a framework for real time group communication Its focus is on group conferencing using a shared whiteboard video and chat system Habanero http www ncsa uiuc edu SDG Software Habanero is a framework for sharing Java ob jects with colleagues distributed over the Internet It is similar to Tango where single user applications are transformed into multi user shared applications using their provided API Finally a Java based implementation of Collaborative Active Textbooks JCAT on algorithms was developed by Digital Equipment Corporation 4 This system which takes advantage of a new feature in Java version 1 1 called Remote Meth
Download Pdf Manuals
Related Search