Implementing Collaborative Applications

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Implementing Collaborative Applications
Prasun Dewan
Department of Computer Science University of
North Carolina CB 3175 Sitterson Hall Chapel
Hill, NC 27599-3175 dewan_at_cs.unc.edu http/www.c
s.unc.edu/dewan
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Infrastructures
Applications
Infrastructures
Applications
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Automation vs Flexibility Tradeoff
Programmer
User
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Favouring the Programmer
Programmer
User
6
Favouring the User
Programmer
User
7
Shared Window System
Application
Stefik 87
Tightly-Coupled Meetings
Easy to Understand
Application-Independent
Automatable
Window
Window
WYSIWIS
Coupling
Audio/Video
User 1
User 2
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Centralized Architecture
XTV (88) VConf (87) Rapport (88) NetMeeting
X Client
Pseudo Server
Pseudo Server
X Server
X Server
User 1
User 2
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Replicated Architecture
Rapport VConf
X Client
X Client
Pseudo Server
Pseudo Server
X Server
X Server
User 1
User 2
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Synchronization in Replicated Architecture
X Client
X Client
Insert e,2
Insert d,1
Pseudo Server
Pseudo Server
X Server
X Server
User 1
User 2
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Migrate Central Client
X Client
Pseudo Server
Pseudo Server
X Server
X Server
User 1
User 2
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Migrate Central Client
Chung Dewan 96
X Client
Pseudo Server
Pseudo Server
X Server
X Server
User 1
User 2
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Shared Window System
Application
- Scroll Wars
Tightly-Coupled Meetings
- Window Wars
Easy to Understand
- No Flexibility
Application-Independent
- Performance
Automatable
- Consistency
Window
Window
WYSIWIS
Coupling
Audio/Video
User 1
User 2
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File System
File
lrwx
Read/Write
Process 1
Process 1
User 1
User 2
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Relational DBMS
M
IDS
L
Fine-Grained Query Language
Database
Insert/Delete/Select
Process 1
Process 1
User 1
User 2
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Replicated Disconnected Databases
Replica
Replica
source determines
read access
delete replication old data replication
replication schedule
IDS
M
IDS
M
destination determines
write access type replication record
replication ACL rep. rep. param. rep.
immediate rep.
Process 1
Process 1
User 2
User 1
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Coda Connection Degree
Data
Server
send update cache
send update
get uncached
Client 1
Client 2
Cache
Cache
User 1
User 2
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Interprocess Communication
Session Manager
register, get peers
Process 1
Process 1
Absolute Flexibility
- No Automation
User 1
User 2
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ISIS Causal and Atomic Broadcast
create_group, join_group, leave_group
P2
P1
ISIS
ISIS
P3
ISIS
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Multiple Views
Model
request
View
View
Window
Window
User
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Multiple Threads in Rendezvous
Model
Multi Views
Prevent starvation
-Two-Phase Comm.
View
View
-Central Arch.
Window
Window
Host 1
Host 2
User 1
User 2
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2-Phase Model-View Protocol
Figure originally appears in 22
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Clock Optimized MVC
Figure originally appears in 22
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Xeroxs Colab. Broadcast Methods
Model
Model
View
View
Window
Window
User 1
User 2
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GroupKit Environment Replication
K1, V1
K1, V1
Environment
Active Environments
P
Q
Multicast Session-based Calls
S
Procedures
U
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GroupKit Open Session Management
K1, V1
K1, V1
K2, V2
K2, V2
I
I
P
R
Q
updateEntrant
userReqNewConf
newUserApproved
Registrar
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Suite Parameterized Generator
Active Variables
C Application
bool validateElem V1(int newVal)
void updateV1 (int newVal)
void updateElemV1 (int index, newVal)
Attributed Interaction Variables
transmit
edit v12
commit
validate
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Text Editor
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Text Editor
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Multiuser Outline
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Outline
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Talk
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Talk Program
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Command Interpreter
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Command Interpreter
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Web
Wide-Area Naming and Sharing
HTTP Server
Form 1
High-level Local UI
Cgi scripts
-Async
-Jittery
Web Browsers
Rendered HTML Document
User 2
User 1
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Implementation Taxonomy
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Single-User Architecture
Model
View
Windows
PC
User 1
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Layered Interaction with an Object
Abstraction
Interactor Absrtraction Representation
Syntactic Sugar
Interactor/Abstraction

• John Smith

• John Smith

Interactor/Abstraction
X

• John Smith

Interactor
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Single-User Architecture
Abstraction
Interactor
Interactor
Interactor
User 1
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Generic Architecture
Abstraction
Semantics
Stem
Version
Version
Branch
Branch
Interactor
Hardware
Interactor
Hardware
User 1
User 2
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Example Layers
Model
View
Windows
PC
User 1
User 2
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Varying Replication Degree
Model
Team Workstation
View
Pure Centralized
Windows
PC
Degree 0
User 1
User 2
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Varying Replication Degree
Model
Shared Window Systems
View
XTV
Rapport
NetMeeting
Centralized
Windows
Windows
Degree 1
PC
User 1
User 2
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Varying Replication Degree
Model
View
Degree 2
Windows
PC
User 1
User 2
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Varying Replication Degree
Model
Degree 3
Hybrid
Windows
PC
User 1
User 2
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Varying Replication Degree
Replicated
Divergence Concurrency Distribution -
Duplication - Non-
Idempotent Operations
Windows
PC
User 1
User 2
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Varying Concurrency Degree
Model
Windows
Serial
PC
Degree 0
User 1
User 2
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Varying Concurrency Degree
Model
Semi-concurrent
Degree 1 lt R
Windows
PC
User 1
User 2
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Varying Concurrency Degree
Model
Concurrent
Suite Rendezvous Weasel Clock
Degree Replication Degree
Fairness Concurrency Distribution -
Scheduling Overhead - Programming Overhead
Windows
PC
User 1
User 2
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Varying Distribution Degree
Model
Windows
Single-Site
PC
Degree 0
User 1
User 2
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Varying Distribution Degree
Model
Rendezvous
Semi-Distributed
Degree 1 lt Concurrency Degree
Windows
PC
User 1
User 2
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Varying Distribution Degree
Distributed
Model
Degree Concurrency Degree
Suite Weasel Clock
Local Response Compact
Communication - Programming Overhead - Pointers
Windows
PC
User 1
User 2
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Varying Collaboration Awareness
Model
Team Workstation
Windows
Hardware-support
PC
Degree 0
User 1
User 2
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Varying Collaboration Awareness
Model
Shared Window Systems
XTV
Rapport
NetMeeting
Window-support
Windows
Degree 1
PC
User 1
User 2
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Varying Collaboration Awareness
Model
Suite Weasel Clock
Sharing Flexibility - Interaction Flexibility
Windows
PC
User 1
User 2
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Partitioned Support
Model
Separation of Concerns - Duplication -
Coordination
Windows
PC
User 1
User 2
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Adding Collaboration Awareness
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Colab. Transparent Delegate
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Replication Granularity
Coarse Grained
XTV
Fine-Grained
Suite, DistView
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Replica Naming
Efficient
Reusable
XTV
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Peer-Peer Coupling
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Peer-Peer Coupling
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Peer-to-Peer Coupling
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Display Consistency
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Algorithm
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Algorithm
t (Ii, pi, Ij, pj) if Pi gt Pj t
Ii(Ci, Pi1) elsif Pi lt Pj t Ii(Ci,
Pi) elsif Ci Cj t null
elseif pi gt pj t Ii(Ci, Pi)) else t
Ii(Ci, Pi1)
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Inserting at Same Position
Site 3
Site 1
Site 2
O2 Insert (B, 1)
O3 Insert (C, 1)
O1 Insert (A, 1)
O2 Insert (B, 1)
O3 Insert (C, 1)
A
C
A
B
C
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Tricky Case
Site 3
Site 1
Site 2
O3 Insert (C, 1)
O3 Insert (C, 1)
O1 Insert (A, 1)
O1 Insert (A, 1)
O1 Insert (A, 1)
C
A
C
A
B
C
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Implementing Undo
Full Check Point
Check Point C1s Effects
C1
C1
Full Check Point
Check Point C2s Effects
C2
C2
Full Check Point
Partial Check Point
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Implementing Undo
Full Check Point
Inverse(C1)
C1
C1
Partial Check Point
Inverse(C2)
C2
C2
Partial Check Point
Inverse Commands
C3
Hybrid Approach
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Selective Undo
Ins 1, C
Del 1, C
Del 1, C
Ins 1, A
Ins 1, B
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Multi-Layered Undo
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History Command Object
History
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Distributed Undo
5.0
5.0
6.0
6.0
5.0
5.0
5
6
5
78
Collaborative Undo
5.0
5.0
6.0
6.0
5
6
Requesting Object
Originating Object
79
Composable Support
Model
Collaboration Bus
Composable Logger
Separation of Concerns - Coordination
Windows
PC
User 1
User 2
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Coupling Awareness
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Collaboration Bus
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