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OOFwDPfBDIS O-O Frameworks with Design Patterns for Building Distributed Information Sharing –Dissertation by Björn Eiderbäck –NADA/KTH, 3/2001 –Presentation.

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Presentation on theme: "OOFwDPfBDIS O-O Frameworks with Design Patterns for Building Distributed Information Sharing –Dissertation by Björn Eiderbäck –NADA/KTH, 3/2001 –Presentation."— Presentation transcript:

1 OOFwDPfBDIS O-O Frameworks with Design Patterns for Building Distributed Information Sharing –Dissertation by Björn Eiderbäck –NADA/KTH, 3/2001 –Presentation by Stephen Travis Pope

2 Outline Overview Goals & Definitions The Problems with Patterns Distributed Processing Systems UI Builders The MultiGossip Patterns & Framework Evaluation, Comments & Questions

3 Overview of the Work Background of the team and project IPLab, MultiG COMIC: Shared Obj. Svc, Interface Svc. MMProg Project (DMIB?) OOP & OOD Patterns Distributed Processing for CSCW (a natural combination) The MultiGossip Framework

4 The Thesis Three components: –Survey and R&D questions (70 p) –Solutions and implementations (100 p) –Evaluation and conclusions (24 p) Topical focus: –OOP, CSCW, design patterns, GUI Frameworks, DPE, UIBs

5 Goals of this Work Integrated framework for information sharing Distribution and cooperation via agents Reflexive environment Information sharing techniques New design patterns Use of OO techniques

6 My Comments Pick fights with Björn’s quotes and abuse of basic definitions Complain about the state of the current “pattern frenzy” Sell you all CORBA ORBs Evangelize for Smalltalk Generally know it all better...

7 Basic Definitions Problems: Object, Actor, and Agent Object: encapsulated state and behavior –Has: identity, well-known behavioral interface, possible class relationship Agent: Object with a “thread” –Implies self-directed action, dependency –E.g., Observer, blackboard, Cellular Automaton

8 Service/Object/Agent Semantics Task service Resource manager Method servers(?) Project (meta) agents Weak vs. strong agency a la Kendall

9 Design Patterns Pattern history –Architecture, Eiffel/Smalltalk OOD (reverse architecture or pattern mining) “Pattern describes an abstract problem and the basic structure of a solution” Ways of describing OO design patterns (formally) Wegner: “Objects, components, and frameworks cannot be specified by algorithms.” (hogwash!)

10 The GO4 Pattern Template Several formats: –Name –Intent –AKA –Problem/Motivation –Solution/Applicability –Structure/Participants –Known Uses –Consequences –See also (relatives) Augmented by: –Free text –UML Diagrams Class relationships Action sequences E/R diagrams –Code examples

11 Example: Dependency Name/AKA: Observer, constraint, publish/subscribe, data-flow Context/Intent: dist. systems Motivation : indep. objects + constraint Forces: loose coupling Solution/Structure/Applicability: dependency mechanism Known Uses: MVC, Observer/-able

12 GO4 Pattern Relationships Purpose CreationalStructuralBehavioral Class Factory MethodAdapterInterpreter Scope Template Method Object Abstract FactoryAdapterResp. Chain Scope BuilderBridgeCommand PrototypeCompositeIterator SingletonDecoratorMediator FaçadeMemento FlyweightPublish/Subscribe GlueState ProxyStrategy Visitor

13 Structure of Patterns & Pattern Decomposition Dependency/Observer/P-S/Constraint –Model is-a observable (has-a dependents) –View implements updating –Transparent forwarding between Model and (0-n) (1-n) Views Adaptor/Holder/DynamicValue/Wrapper/ Proxy/Bridge –Holder implements external protocol (has-a value) –Value does something else –Transparent forwarding between Holder and (0-n) (1) Values Does this help to differentiate them?

14 Pattern Issues Q: Is call-back a pattern? What about dependency or adaptation? Q: What’s the (formal) difference between tool kits, libraries, and frameworks? Q: Is MVC a pattern or a framework? (p. 75) Q: Are all frameworks architectural?

15 Pattern Hierarchies and Primitives Are there primitives and notations that we could use to formally describe the construction and composition of patterns and the relationships between them? Well, are there?

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17 Distributed Processing Defined Multiple processors without shared memory(?) Communicate by sending messages via some network Focus on behavioral interfaces

18 Distributed Processing “Light” Managing concurrency, multi- processing, and physical distribution Requirements –Network, low-level protocols (assumed) –XDR: external data representation –RPC/RMI: remote method invocation These may be described in an IDL –A few basic services (naming, 1:n events)

19 Distributed Processing Issues XDR and marshalling (pass-by- reference supported?) RMI modes: sync, blocking, 1:n, call- back, etc. IDL: fcn. prototypes, exceptions, interface class hierarchy, QoS Run-time configuration and management

20 DPE Systems & Semantics Actors & Laws of Parallel Processing Concurrent OO Languages –ABCL/1 –ConcurentSmalltalk DST/CORBA –Heavy-weight –Possibly transparent

21 Required Services (BE) Required –Naming –Messaging (RMI) –Life-cycle Optional –User registration –Trading –Transactions/concurrency –Events –Persistency

22 The Problems with Sharing Concurrency and threading problems Session state and persistency problems Distributed garbage collection Fault-tolerance

23 The Goal of DPE Transparency across –Access –Location –Concurrency* –Replication* –Faults –Migration* –Performance –Scaling

24 Architectural Style in DPE Information issues –Centralized vs. replicated Communication Issues –Host-terminal –Client-server –Broadcast data –Batch communication –Peer-to-peer? –Others?

25 OOP and DPE Natural mix –Data-hiding and encapsulation –Behavior via message-passing –Focus on interfaces and shared behavior –Various “transparencies” But: –No explicit call-by-reference –No answers for concurrency, distribution, 1:n events, etc.

26 GUIs and Frameworks GUI Architecture and OO patterns Impact on the design of widget sets UI Builders and GUI construction VisualWorks: –Merge of display list graphics and view layout –All connections via adaptors –All “adornment” via wrappers –Run-time GUI construction

27 UI Builder Semantics Graphical configuration “Wiring” Complexity and scaling VisualWorks: –Layout and graphical constraints –Dialogs for complex connections, pre/post- conditions, etc. –Too complex for simple tasks, but scales well to very complex GUIs

28 CSCW Collaboration across place (physical/geographical distribution) Collaboration across time (off-line partnering) Many terms: messaging, conferencing, co-authoring, etc. Special vs. custom tools

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30 Information Sharing Patterns Viewing patterns Shared access patterns Transport patterns Extension patterns Migration patterns Distribution patterns Issues: location, access, replication, consistency, views and interfaces, etc.

31 Viewing patterns Multiviewing – separate semantics and presentation (MVC, etc.) Shared view – identify shared state as semantic (tight coupling, WYSIWIS) Partly-shared view – divide semantics and presentation, I and O (WYSIWIMS) Different outfits – configurable presentations (medium coupling) Sharing through objects – shared state as separate object (loose coupling) (Fig p. 87)

32 Shared access techniques Transparent distribution (the goal) Transparent object locations (using a mediator/adaptor) Two-tier architecture (but no implied hierarchy, may be P2P) Three-tier architecture (“shared business objects”) Splitting semantics from presentation (many options)

33 Transport patterns Communicating changes to replicates – several approaches, standard fare Message-passing – loose coupling State-poking – abstract/composite setters Meta-model – just an object! (or a component) (Fig p. 95)

34 Distribution patterns Marshalling – serialization, streaming Messenger – proxy, forwarder Low-level connection – ORB + IIOP High-level connection – API based on LLC Arriving back at the origin – blocking calls Mother – DPE Manager Coping with errors – exception propagation Providing undoable actions – no solution!

35 Extension patterns Template method – pluggable (or parameterized) behavior, see pluggable MVC Aggregation with black box – COM composites, JavaBeans

36 Migration patterns Proxy – adaptor? forwarder? wrapper? Adaptor for distribution – see above...

37 Architectural Guidelines Dynamic architecture Indirect Use metaclasses Events and notifications Use adaptors Encapsulate Migration and agents Are these patterns?

38 Architecture for Information- Sharing Applications Technical/Design requirements –OO aesthetics –Structured design rules Required services –Naming, trading, transaction, life-cycle –History, versioning, locking, persistency Applied patterns Proposed architecture

39 Conceptual Components (p. 144) Comm. Infrastructure (L/HLC, RMI) Messaging system (sync) Server & clients Services (required services) Agents, mobile objects Client application

40 Architectural Guidelines Structural advice (malleable) Recommended patterns (factory, metaclass, adaptors, etc.) Recommended design techniques (transparency, mobility) Central components (communication, RMI, obj. manager, naming svc., transaction/migration, etc.)

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42 Integration Easy! (given a sophisticated enough OO development platform...)

43 MultiGossip: A DMIB Implementation Issues –Naming and identifiers –RMI mechanisms (Marshalling and protocols) –Distributed instances –Syntax (ST80) Examples (p. 180 ff)

44 Remote Message Objects Message ID Receiver Do reply Acknowledge Timestamp

45 Evaluation of MultiGossip Controllability Support for Experimentation Extensibility/Flexibility Active services Malleability Support for various media Smooth integration into programming environment

46 Assessment Useful for prototyping Scalable Transparent Controllable Safe and reliable Development speed Performance and latency Coverage Expressive Useable

47 Evaluation Criteria Object sharing Distributed error handling Extension Port to new version of platform IB adaptation Core extension

48 Building tools Chat Browsers Paint Pong IP (video) phone Window copying Async. Tools

49 Discussion Server vs. loose-coupling Homogeneous protocols Casual vs. server-based connections Persistency Integration with environment MM object integration Extending ST interaction techniques

50 Who Cares? Who needs this? (We do!) –Internet since 1980, WWW since 1992… –Still depressing scarcity of new applications. –CORBA, COM, etc. are still hard to use for building truly novel (MM) applications (see, e.g., our work at CREATE) What’s the contribution of this work? –Important new patterns and their impact on architecture analyzed –Design and implementation alternatives assessed and MG decisions justified

51 Goals of this Work Integrated framework for information sharing Distribution and cooperation via agents Reflexive environment Information sharing techniques New design patterns Use of OO techniques

52 If he started today… CORBA (??) Java? Squeak/Nebraska VR frameworks HPDM/DPE/VRUT framework Other relevant technologies

53 Conclusions This work is relevant. It makes significant contributions to the field. I suggest a series of articles based on the pattern formalisms, concrete patterns, architectural comments, and system overview. Bravo, Björn!

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