Implementing Collaborative Applications Prasun Dewan Department of Computer Science University of North Carolina CB 3175 Sitterson Hall Chapel Hill, NC 27599-3175 dewan@cs.unc.edu http:/www.cs.unc.edu/~dewan Dewan CS 290-063 1
Infrastructures Applications Infrastructures Applications Dewan CS 290-063 2
Evaluation Criteria • Flexibility • Automation • Efficiency • Reuse of Existing Code Dewan CS 290-063 3
Automation vs Flexibility Tradeoff Programmer User
Favouring the Programmer Programmer User
Favouring the User Programmer User
Shared Window System Stefik ‘87 + Tightly-Coupled Meetings Application + Easy to Understand + Application-Independent + Automatable WYSIWIS Window Window Coupling Audio/Video User 1 User 2 Dewan CS 290-063 7
Centralized Architecture XTV (‘88) VConf (‘87) Rapport (‘88) X Client NetMeeting Pseudo Server Pseudo Server X Server X Server User 1 User 2 Dewan CS 290-063 8
Replicated Architecture Rapport VConf X Client X Client Pseudo Server Pseudo Server X Server X Server User 1 User 2 Dewan CS 290-063 9
Synchronization in Replicated Architecture abc abc dabc aebc deabc daebc X Client X Client Insert d,1 Insert e,2 Insert e,2 Insert d,1 Pseudo Server Pseudo Server Insert d,1 Insert e,2 X Server X Server User 1 User 2 Dewan CS 290-063 10
Migrate Central Client X Client Pseudo Server Pseudo Server X Server X Server User 1 User 2 Dewan CS 290-063 11
Migrate Central Client Chung & Dewan ‘96 X Client Pseudo Server Pseudo Server X Server X Server User 1 User 2 Dewan CS 290-063 12
Shared Window System - Scroll Wars + Tightly-Coupled Meetings - Window Wars Application + Easy to Understand - No Flexibility + Application-Independent - Performance + Automatable - Consistency WYSIWIS Window Window Coupling Audio/Video User 1 User 2 Dewan CS 290-063 13
File System Grove Outline IBIS Arguments lrwx File GroupDraw Drawing Notes Document Prep Document Read/Write Process 1 Process 1 - Large- + Sharing Grained + Persistence - Connected User 1 User 2 + Access, - Async Conc. Control Dewan CS 290-063 14
Relational DBMS Author, Category, Status and Awareness Info M IDS + Fine-Grained L Database Insert/Delete/ + Query Select Language Process 1 Process 1 User 1 User 2 Dewan CS 290-063 15
Replicated Disconnected Databases “Replica” “Replica” DC -> C source determines rep. schedule read access IDS M IDS M delete replication old data replication replication schedule destination determines write access type replication Process 1 Process 1 record replication ACL rep. rep. param. rep. User 2 User 1 immediate rep. Dewan CS 290-063 16
Coda: Connection Degree Data Server SC send update & cache send update SC DC -> SC send updates & get uncached WC SC cache WC trickle updates WC send updates DC -> SC Cache Client 1 Client 2 Cache User 1 User 2 Dewan CS 290-063 17
Interprocess Communication Session Manager register, get peers Process 1 Process 1 + Absolute - No Flexibility User 1 User 2 Automation Dewan CS 290-063 18
ISIS: Causal and Atomic Broadcast cbcast_group t( m2) < t (m1) create_group, join_group, leave_group abcast_group t (m1) < t( m1’) t (m1’) < t (m1) P2 P1 m1 m1 ISIS ISIS m2 m1 m2 commuting m1 = color red operations m1 m2 m1’ = magnify P3 non-commuting m1 = Insert a, 2 m1’ ISIS m1’ operations m1’ = Insert b, 1 Dewan CS 290-063 19
Multiple Views Host 1 Model notify request notify View View Window Window User Dewan CS 290-063 20
Multiple Threads in Rendezvous +Multi Model Multiple Views threads Prevent -Two- View View starvation Phase Comm. -Central Window Window Arch. Host 1 Host 2 User 1 User 2 Dewan CS 290-063 21
2-Phase Model-View Protocol Figure originally appears in [22] Dewan CS 290-063 22
Clock: Optimized MVC Figure originally appears in [22] Dewan CS 290-063 23
Xerox’s Colab. Broadcast Methods Associates/ Associates/ Replicas Replicas Broadcast Association Model Model method bm lm lm View View lm lm lm Window Window User 1 User 2 Dewan CS 290-063 24
GroupKit: Environment Replication K1, V1 K1, V1 Environment Active I K2, V2 K2, V2 Environments I I R P Q all Multicast T S T Procedures Session-based others, Calls U V usernum Dewan CS 290-063 25
GroupKit: Open Session Management +Flexible K1, V1 K1, V1 -Collaboration K2, V2 K2, V2 Aware I I R P Q newUserArrived newUserArrived updateEntrant Session userReqNewConf Session User 1 User 2 Manager Manager new newUserApproved new invite invite Registrar Dewan CS 290-063 26
GroupKit Multicast Code & Events Shared Idea List proc insertIdea idea { insertColouredIdea blue $idea gk_toOthers ’’insertColouredIdea red $idea’’ Event Handlers gk_bind newUserArrived { makeChatWindow %U } proc makeChatWindow usernum { ... } Dewan CS 290-063 27
GroupKit Shared Environments Group Hello World gk_initConf $argv gk_defaultMenu .menubar pack .menubar -side top -fill x gk_newenv -bind -share message message greetings ’’Hello World’’ button .hello -text ’’Hello World’’ -command { message greetings ’’[users local.username] says hello!’’} pack .hello -side top message bind changeEnvInfo .hello configure -text [ message greetings ] after 2000 {.hello configure -text ’’Hello World’’} } Dewan CS 290-063 28
Suite: Parameterized Generator Active int[] v1 Variables C Application bool validateElem V1(int newVal) void updateV1 (int[] newVal) void updateElemV1 (int index, newVal) Attributed v1[2] v Interaction V1[ update(v2, newVal) Variables 2] int v1 (widget = w1, int v1 (widget = w2, Dialogue valueCpld = true, valueCpld = true, Managers viewCpld = false, sync viewCpld = true, sync = incr, access = “rw”) v1[2] = explicit, access = “r”) edit v1[2] transmit validate commit Dewan CS 290-063 29 User 2 User 1
Text Editor Dewan CS 290-063 30
Text Editor /*dmc Editable String */ String text = "hello world"; Load () { Dm_Submit (&text, "Text", "String"); Dm_Engage ("Text"); } Dewan CS 290-063 31
Multiuser Outline Dewan CS 290-063 32
Outline /*dmc Editable Outline */ typedef struct { unsigned num; struct section *sec_arr; } SubSection; typedef struct section { String Name; String Contents; SubSection Subsections; } Section; typedef struct { unsigned num; Section *sec_arr; } Outline; Outline outline; Load () { Dm_Submit (&outline, "Outline", "Outline"); Dm_Engage ("Outline"); } Dewan CS 290-063 33
Talk Dewan CS 290-063 34
Talk Program /*dmc Editable String */ String UserA = "", UserB = ""; int talkers = 0; Load () { if (talkers < 2) { talkers++; Dm_Submit (&UserA, "UserA", "String"); Dm_Submit (&UserB, "UserB", "String"); if (talkers == 1) Dm_SetAttr ("View: UserB", AttrReadOnly, 1); else Dm_SetAttr ("View: UserA", AttrReadOnly, 1); Dm_Engage_Specific ("UserA", "UserA", "Text"); Dm_Engage_Specific ("UserB", "UserB", "Text"); } } Dewan CS 290-063 35
Command Interpreter Dewan CS 290-063 36
Command Interpreter /*dmc Editable CmdSeq */ typedef struct { String Cmd, Result; } CmdRec; typedef struct { unsigned num; CmdRec *cmd_arr; } CmdSeq; CmdRec Init = {"", ""}; CmdSeq CmdList = {1, &Init }; void Execute (cmd_name, val) char *cmd_name; String *val; { int index; char output_name[1024]; char *result; sscanf (cmd_name, "(((CmdList)[%d]).Cmd)", &index); sprintf (output_name, "(((CmdList)[%d]).Result)", index); /* execute command using popen() and capture output */ result = ExecuteCommand (*val); Dm_Update (output_name, "String", &result); Dm_SequenceElementAppend ("CmdList", "CmdRec", &Init); } Load () { Dm_Submit (&CmdList, "CmdList", "CmdSeq"); Dm_SetAttr ("Type: String", AttrAcceptOnReturn, 1); Dm_SetAttr ("Type: String", AttrUpdateProc, Execute); ... Dm_Engage ("CmdList"); } Dewan CS 290-063 37
Web +Wide-Area Naming and Sharing HTTP Server Form 1 +High-level update Local UI Cgi scripts -Async -Jittery get notify get Web Rendered Form 1 Display Browsers HTML Form 1 Display Document edit form1 commit Dewan CS 290-063 38 User 2 User 1
Implementation Taxonomy X Client X Client X Client Pseudo Server Pseudo Server Pseudo Server Pseudo Server X Server X Server X Server X Server User 1 User 2 User 1 User 2 lrwx File Model View View Process Process Window Window 1 1 Host 1 Host 2 User 1 User 2 User 1 User 2 Dewan CS 290-063 39
Single-User Architecture Model View Toolkit Windows PC User 1 Dewan CS 290-063 40
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