Taxonomies of Collaborative Applications Prasun Dewan Department - - PowerPoint PPT Presentation

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Taxonomies of 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

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• 7. Application Taxonomies
• Ellis’s Time Space
• Ellis’s Common Task/Shared Environment
• VR Taxonomy
• Malone’s Taxonomy

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Ellis’s Time Space Taxonomy

Email File System Bulletin Board Augmented Reality Same Time Same Space Different Space Grove MUD Tivoli Ventura Different Time

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RTCAL Vs Electronic Class Room

Proposal: 10am Vote: No Public Appts Public Appts Topic, Participants Chair, Controller

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Ellis’s Shared Environment / Common Task Dimension

Electronic Classroom Time Sharing Environment Software Review System Mail Common Task Shared Environment

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IBIS Vs Talk Vs Shared File

*I: Which processor should be used ?P: Processor A AS: Fast *P: Processor B AS: Cheap, already in use

* +

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Smith’s Dimensions

• Information Type

– intangible private, ephemeral, tangible instrumental, tangible target

• Collaboration Time

– seconds, minutes, hours, days, weeks, months, years

• Space:

– office, floor, site, 1-hour travel, 1-day travel

• Agents

– people, informal coalitions, teams, team collections

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IBIS Vs Email

Processor 2/24/99 Which one? (John Smith, responses) 2/25/99 Processor A (Mary Lowe, 1 response) 2/26/96 Processor B (Joe Doe) Meeting Time 2/24/96 10am? (Mary Lowe, 1 response) *I: Which processor should be used ?P: Processor A AS: Fast *P: Processor B AS: Cheap, already in use

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Malone’s Coordination Taxonomy

Coordination Goal Goal Decomposition Task Assignment Recursive Allocation Synchronization Sequencing 1 Facilitates Coordinator Information Lens RTCAL Group Decision Making Proposing Alternatives Evaluating Alternatives 2 IBIS, PREP, Quilt Communication Transporting Messages Routing 3 email, ActionWorkflow Perception of Common Objects 4 Grove, CES, RTCAL

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Hydra vs MAJIC MUDS Vs DIVE

User 2 User 3

John has entered the room (hear footsteps) John says, “Hi everyone”

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Benford’s VE Taxonomy

Degree of Artificiality Degree of Transportation

• Augmented

Reality

• Physical

Meeting

• Telepresence
• Immersive

CVEs

• Hydra
• Video

Walls

• Video

Conference

• Shared

Application & Video Conf.

• MAGIC
• Projected

CVEs

• Desktop

CVEs

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Concurrency Control

• RTCAL
• Grove
• CES
• GroupDraw
• Floor Control
• No Control
• Tickle Locks
• Optimistic

Locks

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Flexible Model of Collaboration

Application Window Version 1 User 1 User 2 Coupling Window Version 1 Session Management User Merging Undo/Redo Awareness CC/AC

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Design Dimensions

• Session Management
• Coupling
• Concurrency Control
• Access Control
• Undo/Redo
• Merging
• Awareness

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Session Management

User 2 User 3

message from dewan, type talk dewan to join John has entered the room (hear footsteps) John says, “Hi everyone” talk jbs Faculty Meeting 290 Lecture Distinguished Lecture

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Session 1 App1 App2

Session Management Operations

User 1 Join/Leave (User 2) User 2 Create/ Delete (Session 1) Add/Delete (App3) App3 Issue: How are these

• perations invoked?

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Session Management

• Telephone
• Talk
• Menu System
• MUDs
• DIVE
• Invitation
• Invitation
• Name-based
• Room-based
• Aura-based

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Joining in Explicit Sessions

App2 App3 User 1 User 2 Session 1 Join User 2 App1 App2 App3 User 1 User 2 Session 1 User 2 Invite Accept Name-based Joining Invitation-based Joining Rendezvous GroupKit RTCAL XTV Joining N App. Easy & General Applications Flexible Joining Auto Notification Creator Controlled App1

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Implicit Sessions

• Artifacts being edited
• Location in rooms
• Intersection of auras in virtual

environment

Session Joining/Leaving Side Effect of:

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Design of Collaboration Functions

• Session Management
• Coupling
• Concurrency Control
• Access Control
• Undo/Redo
• Merging
• Awareness

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Awareness Examples

Outline Title

• 1. Readable and writeable item

1.1 Also readable and writeable *.Shared readable and writeable * .* Shared readable

Editing paper xxxx yyyyy

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Awareness

App. I/O I/O Version 1 Version 2 Coupling Awareness Others Awareness

• f Others

Physical/Computer Environment Physical/Computer Environment User 1 User 2

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Awareness Purpose

Location Current Tasks Potential for Interruptibility Presence of Coworkers Context for Smalltalk Curiosity

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Awareness Dimensions

Shared? Degree? When? History? User 1 User 2

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Subject Application Object Intermezzo Potholes CAVECAT, Cruiser GroupDraw, XTV Intermezzo Contact Grove, GroupDesign GroupDesign PREP, Active Diff

Shareable Information: Edward’s Model

Login, Name, Home, Shell, Office, Phone, Plan, Voice, Photo Physical Location, Appearance, Gestures, Speech Virtual Location Virtual Gestures Application, Start & Idle Time, Process and Display Host Identification, Type, Value, Attributes, Lock Status Command Location Size Diff

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Awareness Degrees

Subject General Location < Specific Location Pseudo Name < Real Name < Photo, Voice Audio Volume Levels Application Editor < Emacs Object A command was invoked on a nearby object The edit command was invoked on a nearby object The edit command was invoked on this object (The new remote value of this object is ‘the brown fox’) The new remote value of this object is ‘the brown fox’ The remote value replaces the ‘dog’ in the local value with ‘fox’ Macro Chris is at (0,0) Chris is interacting with Emacs Chris is editing this paragraph Nearness Event Peripheral Full Diff Subject Application Object GroupDesign MASSIVE MASSIVE MASSIVE PREP MASSIVE

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Coarseness of Pinpointing

Section Paragraph Sentence Word Section Paragraph Sentence Word Diff Diff Her bowl is over there, by the truck Her bowl is over there, by the car Sentence- Level Diffing car truck Word-Level Diffing

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Additional Differencing Parameters

% Differences Inserted Length

• Max. % Differences

Distance to Look

• Dist. to Concatenate
• DIFF. PARAMETERS

Precent Differences < Max. Percent Differences Inserted Length < Max. Distance to Look for Commonalities Recursion Criteria The quick brown fox jumps over the lazy cat The slow brown dog jumps over the lazy cat quick brown fox slow brown dog quick, fox slow, dog Word-level Diffing

• DIFF. PARAMETERS

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When Awareness Event Shared

Instantly Periodic Explicitly Retrieved Audio Video Diff Snapshots Diff Plan CAVECAT Active Diff Portholes PREP Finger

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History of Events Shown

Current Value Since Last Access Since Conference Start GroupDesk REPLAYABLE WYSNIWIST

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Design of Collaboration Functions

• Session Management
• Coupling
• Concurrency Control
• Access Control
• Undo/Redo
• Merging
• Awareness

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Coupling Examples

File save load Mail send receive Sync Talk h hel h hel Async Talk hi hello hi hello

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RTCAL Vs GroupKit

Public Appts Private Appts Public Appts Public Appts Public Appts

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Coupling Design Space

Sync Talk ASync Talk Mail File GroupDraw

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Sync Vs Async Talk

My Text Your Text My Text Your Text

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Flexible Coupling

My Text Your Text My Text Your Text communicateOn: {Keystroke, Return}

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Fine-grained Coupling

My Text Your Text My Text Your Text

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Distributed Control

My Text Your Text My Text Your Text

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Produced Exported

Coupling Principle

Imported Shared Max(T1, T2) (T1) (T2) (T0)

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Distributed Control

My Text Your Text My Text Your Text Keystroke < Return communicateOn = Max (TransmitOn, ListenOn)

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Shared Text

Text Text Asymmetric Control communicateOn : {Keystroke, Return, Delete) Keystroke < Return, Delete

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File-based Coupling

Text Text File Commit Load communicateOn: {…, Committed}

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Correctness-based Coupling

int num, num1 = 0 Text File Unparsed

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Correctness-based Coupling

int num; num1 = 0 Text File Parsed

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Correctness-based Coupling

int num1; num1 = 0 Text File Validated

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Correctness-based Coupling

int num1; num1 = 0 Text File communicateOn: {Raw, Parsed, Validated, Committed} Commit Raw < Parsed < Validated < Committed

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Time-based Coupling

int num1; num1 = 0 Text File communicateOn: {Period, Time) Commit

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Mail-based Coupling

Text Text File Commit Load communicateOn: {…, Send, Receive)

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Mail-based Coupling

Text Text File Commit Load transmitOn: {..., Commit, Send) Buffer listenOn: {..., Commit, Receive)

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Sharing Objects

Version Version Base Commit Load transmitOn: {…, Increment, Completion) Buffer Completion= Return || Mouserelease Increment = Keystroke || Mousedrag

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Suite Communication Model

Version Version Base Buffer

TTime LTime TPeriod LPeriod TOn TCorrectness LOn LCorrectness

Op Cur. Correctness Value Transmitted if: (Op, CurCorr) >= (TOp, TCorr) (LOp, LCorr) Value Received When Min (LPeriod, LTime) Receive Executed

Inc < Complete < Send Raw < Parsed < Valid< Comm

LPeriod, LTime: {T, ListenNow}

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Coupling Objects Vs Versions

X = 6 X = 5 X = 5 X = 5 Y = 25

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Coupling Objects Vs Versions

Hello world hello World hello world Hello John Hello John Goodbye John My Out Message /Input Line John’s Inbox/ Chat History

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RTCAL Vs GroupKit

Public Appts Private Appts Public Appts Public Appts Public Appts

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Suite Sharing Model

Version Version Base Buffer

Value TOp Font Cursor Widget Color RW Scrollbar

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Suite Sharing Model

Version Version

Value Value Font Color Font Color TOp TCorr TOp TCorr ValueC ValueC FormatC ValueC FormatC FormatC CommC CoupleC

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Coupling Policies

Semantics ValueC = T Syntax FormatC = T View ViewC = T Implicit TOn < Send Explicit TOn = Send Synchronous TOn, LOn = Inc ASynchronous TOn > Inc WYSIWIS *C = T Ton, Lon = Inc Serializable TCorr = Committed

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Design of Collaboration Functions

• Session Management
• Coupling
• Concurrency Control
• Access Control
• Undo/Redo
• Merging
• Awareness

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Concurrency Control Examples

• RTCAL
• Grove
• CES
• GroupDraw
• Sync
• Floor Control
• No Control
• Tickle Locks
• Optimistic,

Selection- based Locks

• Optimistic

Transactions

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Concurrency Control Goals

• Consistency
• Concurrency
• Performance

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Concurrency Control Dimensions

• Free Vs Controlled
• Correctness Criterion
• User-Transaction Mapping
• Sharing and Inconsistency Detection Time

– Lock Granularity – Locking/Unlocking Actions

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Free Vs Controlled

• WYSIWIS Vs WYSINWIS Coupling
• Small Vs Large Teams
• Efficiency

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Concurrency Control Correctness

T1

• 11
• 12

T2 T3

• 21
• 22
• 31
• 32

Actual Schedule

• 31 o21 o11o22 o12 o32

T3 T2 T1 Serial Schedule =

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Concurrent Drawing

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Concurrent Drawing

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Concurrent Drawing

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Non-Serializable: Reject

T1 R(Drawing) W (Drawing) T2 R (Drawing) W (Drawing)

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Finer-Granularity: Serializable

T1 R(Line) W (Line) T2 R (Rectangle) W (Rectangle)

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Non- Serializable: Accept

T1 R(Drawing) W (Line) T2 R (Drawing) W (Rectangle)

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Concurrent Drawing

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Concurrent Drawing

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Concurrent Drawing

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Type-Specific: Reject

T1 R(Line) Rotate (Line) T2 R (Line) Color (Line)

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Type-Specific: Serializable

T1 R(Line.Bounds) Rotate (Line) T2 R (Line.Color) Color (Line)

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Concurrent Drawing

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Concurrent Drawing

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Concurrent Drawing

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Concurrent Drawing

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Schedule

T1 R(Drawing) W (Line) T2 R (Drawing) W (Rectangle) R(Drawing) W (Line)

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Splitting Transaction

T1 R(Drawing) W (Line) T2 R (Drawing) W (Rectangle) R(Drawing) W (Line) T3

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Joining Transactions

U1 R(Drawing) W (Line) U2 R (Drawing) W (Rectangle) R(Drawing) W (Line)

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Nested Long Transactions

Program Module L, M Module N, O Module L Module M Proc P Proc Q Team A Team B rogrammers Testers A B

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Implicit Transaction Operations

Select Object => Begin Transaction Unselect Object => End Transaction Start Dragging => Begin Transaction Stop Dragging => End Transaction Stop Dragging => Begin Transaction Move Object End Transaction

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Implicit Transaction Operations

Press Key => Begin Transaction Release Key => End Transaction Insert Char => Begin Transaction Return, Delete Char, Timeout => End Transaction Sync Couple => Join Transaction Async Couple => Split Transaction

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Design of Collaboration Functions

• Session Management
• Coupling
• Concurrency Control
• Access Control
• Undo/Redo
• Merging
• Awareness

Collaborative Application

Application Window Window User 1 User 2

Access Control

Application Window Window User 1 User 2

Meta Access Control

Application Window Window User 1 User 2 Authorizer Meta Authorizer

Access Control Prevents

Alice’s Exam Alice Bob’s Exam Bob

Couple

Security Violations

Listener 1 Turing Lecture Session

Doug Engelbart

Create Join

Listener 1000

Join

Overuse of Scarce Resources

Bob’s Proposal

Read Write

Mistakes Alice

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Access Control Principles

• Total Mediation
• No Secret Design
• Least Privilege (Need to Know)
• Ease of Use

Traditional Protected Objects

matmult.java Matrix matmult.java Graphics Button.java R W X R W I D M

Traditional Access Control

matmult.java Matrix matmult.java Graphics Button.java R W X R W I D M

Collaborative Systems

matmult.java Matrix matmult.java Graphics Button.java R W X R W I D M matmult.java public int i; void f() { public int i; void f() { void g() { int i, // tricky void g() make private! Data Rights Coupling Rights Buffer Rights Numerous Rights! UI Rights!

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• Colab. Objects & Rights

Session JoinSessionR ReadSessionR ModifySessionR RemoveParticipantR DeleteSessionR Window CursorR ScrollR ResizeR MoveR No Leave SessionR Apply to Coupled windows

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Model/View Rights

Semantic Object UpdateR WriteR InsertR DeleteR ReadR Interaction Object HideR ElideR SelectR TitleR FontR ColorR IndentR ValueCR ViewCR FmtCR TIncR TRawR LIncR Data Rights Coupling Rights View Rights

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Optimistic Access Control

Semantic Object

• UpdateR

+WriteR +InsertR +DeleteR +ReadR Interaction Object

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Pessimistic Access Control

Semantic Object

• UpdateR

Interaction Object

• WriteR
• InsertR
• DeleteR
• ReadR

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Traditional Access Matrix

Objects

Subjects rights

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Extended Access Matrix

Objects + groups

Subjects + groups rights + groups

Suite Access Control

AnAnnotation +CoupleR Annotator +ScrollCoupleR +DataCoupleR Bob Alice Alice’s Annotation Bob’s Annotation Bob Alice Access List Entry

Suite Access Control: Implications

UpdateR WriteR InsertR DeleteR ReadR

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User Groups as Protected Objects

Role TakeR LeaveR DeleteR

Suite Access Control: Implications

+TransmitIncrementR +TransmitCompleteR +TransmitPeriodicR +TransmitExplicitR +ModifySessionR +CreateSessionR +ReadSessionR

Roles, Right Inheritance, Implications, User- defined rules

Suite Meta-Access Control: First- Class Access Control Objects

Protected Object User Authorizer Access Control Roles, Right Inheritance, Implications Rights Meta Rights Meta Control

Roles, Right Inheritance, Implications, User- defined rules

Suite Meta-Access Control: First- Class Access Control Objects

Protected Object User Authorizer Access Control Roles, Right Inheritance, Implications Rights Meta Rights Meta Control Bootstrapping!

Build Access-Control Class

Protected Object User AC

Instantiate Class Again

Protected Object User* User AC AC*

Must Instantiate Again

Protected Object User* User AC AC* User** AC**

Infinite Recursion

Protected Object User* User AC AC* User** AC** User*** AC***

Roles, Right Inheritance, Implications, User- defined rules

Stopping Recursion

Protected Object User Access Control Roles, Right Inheritance, Implications

Roles, Right Inheritance, Implications, User- defined rules

Existing Meta Control

Protected Object User Access Control Roles, Right Inheritance, Implications

• wner

central authorizer

Flexible Authorizer Assignment

public int i; void f() { public int i; void f() { No Authorizer

Flexible Authorizer Assignment

public int i; void f() { public int i; void f() { moderator Central Authorizer

Flexible Authorizer Assignment

public int i; void f() { public int i; void f() { Single Owner Alice

Flexible Authorizer Assignment

public int i; void f() { public int i; void f() { Multiple Owners Alice Bob

Partial Authorization

public int i; void f() { public int i; void f() { Alice Bob Professor

Partial Authorization

public int i; void f() { public int i; void f() { Alice Bob Professor Leader

Delegation

Professor TA 1 Exam +CoupleR Students Delegate TA 2 Delegate

Shallow Revocation

Professor TA 1 Exam +CoupleR Students TA 2 Delegate

Deep Revocation

Professor TA 1 Students TA 2

Proportional Overhead

Programming Contest Brainstorming Military Programming

Incremental Migration Path

Programming Contest Brainstorming Military Programming

Economy of Concepts

Protected Objects Meta Control Access Control

Fine-Grained Meta Rights => Partial Authorization

+CoupleR +CoupleR* +DataR +DataR* +SessionR +SessionR*

Automatically-Generated Include and Imply Relationships => Proportional Overhead, Economy

+ModifySessionR +CreateSessionR +SessionR +ModifySessionR* +CreateSessionR* +SessionR*

Authorizer Problem: Owner

+CoupleR* public int i; void f() { Bob (Object Creator) Alice (Application Starter) +ScrollR +ScrollR* +CoupleR

Authorizer Problem => Ownership

Bob (Object Creator) public int i; void f() { Alice (Application Starter)

Owner Lists => Joint Ownership

Bob (Object Creator) Alice Bob +OlistR +OlistR* public int i; void f() { Alice (Application Starter)

Default Ownership Semantics

+OwnerR +OListR, OListR*, AllR, AllR* Alice Bob +OwnerR +OwnerR Default Ownership public int i; void f() { OL ~ ACL

Flexible Ownership Semantics => Flexible Authorizer Assgnmt

No authorizer +OwnerR Class Object All AllR* ACL

Flexible Ownership Semantics => Flexible Authorizer Assgnmt

Class Object Administrator Central authorizer AllR* +OwnerR ACL

Total & Partial Delegation => Proportional Cost & Economy

Alice Alice Bob Exam +CoupleR Students Total

Total & Partial Delegation => Proportional Cost & Economy

Alice Alice Bob Alice Bob Exam +CoupleR Students Exam +CoupleR* Exam +CoupleR Students Total Partial

Shallow Revocation

Alice Alice Alice Bob Exam +CoupleR Students Exam +CoupleR Students Total Partial

Shallow Revocation

Alice Alice Alice Bob Exam +CoupleR Students Exam

• CoupleR*

Exam +CoupleR Students Total Partial

Delegation for Flexible Revocation

Alice Grantee Exam

• CoupleR

Faculty Student Grantee +AddMemberR Bob Grantee +AddMemberR*

Delegation for Flexible Revocation

Alice Grantee Exam

• CoupleR

Grantee +AddMemberR Bob Grantee +AddMemberR*

Delegation for Flexible Revocation

Alice Grantee Exam

• CoupleR

Faculty Student Grantee +AddMemberR Bob Grantee +AddMemberR*

Delegation for Flexible Revocation

Alice Grantee Exam +CoupleR Faculty Student Grantee

• AddMemberR

Bob Grantee

• AddMemberR*

Delegation for Flexible Revocation

Alice Grantee Exam +CoupleR Student Grantee

• AddMemberR

Bob Grantee

• AddMemberR*

Partial Undo

Delegation for Flexible Revocation

Alice Grantee Exam

• CoupleR

Grantee

• AddMemberR

Bob Grantee

• AddMemberR*

Total Revocation

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Example Policies

Drawing +AllR All

Free for All

Outline +InsertR All

Grove

+OwnerR +DataR,+DataR*

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Examples (Contd.)

User A Buffer +ReadR User B

2-Way Talk

+AllR User A User B Buffer +ReadR User A +AllR User B User N’s Buffer

N-Way Chat

+AllR User N Transcript +ReadR All

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Examples (Contd.)

Program Name +WriteR Chairman

Software Inspection Tool

+AllR All Program +ReadR All +FormatR, FormatR* Formatter

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Examples (Contd.)

Class Object

Programming Contest: Exam Phase

+ReadR, +AllR* Proctor Program1 +DataR Team1 Team1 +CouplingR (Team1, Proctor) +OwnerR +DataR,+DataR

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Examples (Contd.)

Class Object

Programming Contest: Review Phase

+ReadR, +AllR* Proctor Program1 +DataR Team1 Team1 +CouplingR (Team1, Proctor) +OwnerR +CouplingR (All), +InsertR, +ReadR All +AllR, +AllR* +DataR,+DataR

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Dynamic Role Assignment

I don’t mind sharing my workspace with others during demo day def predicate (subject me context) if date.today() == DEMO-DAY if me.location === “GVU Lab” if me.Activities.member(“Montage”) if subject.location == “GVU Lab” return true

Experience with Meta Control Specifications

• Grove
• Unix
• AFS
• Mail, Talk
• Collaborative Inspection Tool
• Programming Contest Tool (Competition

and Inspection Phases)

1-27 Access Specifications 6 ms Overhead

Experience (contd)

• Graphical Tool for Displaying

Inheritance and Implications

• Use 1-Dimensional Inheritance at

a Time

Summary of Access Control

• Flexible Authorizer

Assignment

• Partial Authorization
• Flexible Delegation &

Revocation

• Proportional

Overhead

• Economy of

Abstractions

• User-Defined Ownership

Semantics

• Fine-Grained Meta Rights
• Indirect Roles
• Inheritance, Implications
• Meta Rights, Owner Lists,

Owner Right

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Undo/Redo: Motivation

• Recover from Self

Errors in 1-User Commands

• Explore Self

Alternatives

• Be more Daring
• Others’ Errors
• System Errors (Conc Inp)
• Colab Commands

– Coupling, Access, …

• Explore Group

Alternatives

• Dare to modify shared

information

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Requirements

• Easy to Use
• Efficient
• Consistency
• Undo Hard to reverse

Action

• Matched to Do
• Undo Undo
• Undo Computation
• Undo remote displays
• Undo of remote

commands

• Undo collaboration

commands

• Compatibility with

single-user models

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Multiuser UndoVs Database Abort

• Consistency

– Cascaded Abort – I/O not Undoable

• System Triggers

Generally

• Initiating User Can

Undo

• All Pending Actions

Undone

• Consistency

– Undoing Remote displays

• User Triggers

Generally

• Any User Can Undo
• Specific Pending or

Committed Actions Undone

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US&R Model

C1 C2 C3 C1 C2 C3 Undo C1 C2 C3 C1 C2 C3 Undo Redo C1 C2 C3 C1 C2 C4 C3 C4 C1 C2 C4 C3 C1 C2 C4 C3 Undo Skip Redo C1 C2 C4 C3

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History Model

C1 C2 C3 C1 C2 C3 Undo C1 C2 C3 C3’ C1 C2 C3 C3’ C2’ Undo C4 C1 C2 C3 C3’ C2’C4 Undo C1 C2 C3 C3’ C2’C4 C4’ Undo C1 C2 C3 C3’ C2’C4 C4’C2’’

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Multi-user Undo Factors

• Single-User Undo
• Coupling
• Access Control
• Broadcast Scheme
• Concurrency Control

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Global, Last-Command Undo

A1 B1 A2 A1 B1 A2 A1 B1 A1 B1 A2 Undo A1 B1 A2 A1 B1 A2

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Disjoint Manipulation

Insert O1 Insert O2 Insert O1 Insert O2 Undo Insert O1 Insert O2 Insert O3 Insert O1 Insert O2 Insert O3

O1 O2

Insert O3

O3

Insert O1 Insert O2 Insert O3 Insert O1 Insert O2 Insert O3

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Concurrent Serialized Interaction

A1 B1 A1 B1 A2 Undo A1 B1 A2 A1 B1 A2 A1 B1 A2 A1 B1 A2 Undo

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Concurrent Non-Serialized Interaction

A1 B1 A1 B1 A2 Undo A1 B1 A2 A1 B1 A1 A2 B1 A1 B1 A2 Undo A2 Entire undo history can be locked

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Non-WYSIWIS Coupling

A1 B1 A1 B1 A2

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Local- Corresponding Undo

A1 B1 A2 A1 B1 A2 A1 B1 A2 B1 A1 B1 A1 A2 Undo B1 A1 A2 Undo

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Cooperative Manipulation

Create O Move O Undo Undo Create O Move O O Create O Move O Exception!

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Selection-based Undo

A1 B1 A2 A3 Undo(B1) A1 B1 A2 A3 A1 B1 A3 A1 B1 A3

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Selection, Corresponding Undo

A1 B1 A2 A3 Undo Undo A1 B1 A2 A3 A1 B1 A3 A1 B1 A3 A1 B1 A3 A1 B1 A2 A3

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Undo Filters

Create O1 Create O2 Move O1 Move O2 Create O2 Move O1 Create O1 Move O2 Filter Blue User Filter Red User Commands Executed

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Undo Filters

Create O1 Create O2 Move O1 Move O2 Create O2 Move O2 Create O1 Move O1 Filter O1 Filter O2 Commands Executed

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Ambiguities in Selection-based Undo

Color Red Color Yellow Color Green Undo (Color Yellow) abc Delete 2, b ac Delete 2, b Insert 2,d adc Delete 2, b Insert 2, d Undo (Delete 2, b

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Asynchronous Commands

A1 B1 A2 A3 Transmit (A2, A3) A1 B1 A1 B1 A2 A3 A1 B1 A2 A3

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Asynchronous Commands

A1 B1 A2 A3 Transmit (A2, A3) A1 B1 A2 A3 T(A2, A3) A1 B1 A1 B1 T (A2, A3)

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Single-User Interaction

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Single-User Undo

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Multi-User Interaction

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Multi-User Undo

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Race Condition: Undo Decision

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Race Condition: Concurrent Change

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Undo by Reference

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WYSINWIS Histories

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Corresponding Undo

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Transmitting Changes

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Undoing Transmission

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Triggering Computations

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Undoing Computation