A Framework to Engineer Communities of Web Services Jamal Bentahar Concordia University (Montreal, Canada) Royal Holloway, University of London July 09, 2007

2 Overview Context and Motivations Communities of Web Services: Definitions Communities of Web Services: Engineering Argumentation between Web Services Conclusion and Future Work

3 Context Web services (WSs): A new breed of Web application Self-contained Self-describing Can be published, located, and invoked across the Web Functions: anything from simple requests to complicated business processes Once a Web service is deployed, other applications (and other Web services) can discover and invoke the deployed service

4 Technologies Web service (WS) Software application identified by a URI XML artifacts: Interface definition and discovering Web Service Description Language (WSDL) Universal Description, Discovery, and Integration (UDDI) registry, ebXML Simple Object Access Protocol (SOAP) SOAP defines a common standard that allows different systems to interoperate

5 Standards and Projects Standards for Services definition, discovery, and security Projects for Web services composition, personalization, and contextualization Composition: A user's request cannot be satisfied by any single, available Web service A composite Web service obtained by combining available Web services may be used

6 Service-Oriented Architecture Service Provider Service RequestorService Broker Bind (SOAP) Publish (WSDL) Find (UDDI) Server ClientNaming Service

7 Motivations Communities of Web services Gathering WSs with similar functionalities (e.g. FlightBooking ) How to initiate, set up, and specify a community of WSs? How to specify and manage the WSs that reside in a community? How to conciliate conflicts within a community and between communities?

8 Motivations What can agent technology do for communities of WSs? The notion of agent: software-based computer system that enjoys the following properties: Autonomy Reactivity Pro-activeness Social ability Interest of agent reasoning and communication capabilities

9 Overview Context and Motivations Communities of Web Services: Definitions Communities of Web Services: Engineering Argumentation between Web Services Conclusion and Future Work

10 Collection of WSs with a common functionality These WSs could have distinct non-functional properties A means for providing a common description of a desired functionality Objective: To ease and improve the process of Web services discovery and composition Communities of WSs

11 Architecture of WSs Communities

12 Operations for Community Management Leaving WS1 Community of Web Services Joining WS3WS8 WS6 WS2 WS7 WS4 WS5 A community of Web services is dynamic by nature: Temporarily Unavailable Resuming operation after suspension

13 Overview Context and Motivations Communities of Web Services: Definitions Communities of Web Services: Engineering Argumentation between Web Services Conclusion and Future Work

14 Community management: 1.Development Functionality definition Master WS deployment: A dedicated Web service plays the role of master for the time being of a community Identifying a Web service from the list of Web services populating a community to act as a master 2.Dismantlement Number of active WSs Operations for Community Management

15 Web services: 3.Attraction UDDI consultation Joining persuasion 4.Retention Active behavior Collaborative environment Operations for Community Management

16 Community Management

17 Master WS leads the community: Inviting and convincing Web services to sign up in the community Checking the credentials of Web services before they get admitted Development

18 A master WS responsibility: Attracting new Web services to and retaining existing Web services in a community Consulting UDDI and checking the functionality description of existing WSs Attraction and Retention

19 Web services in a community should expose a cooperative attitude Web services should be aware of some peers in the community that could replace them in case of failure Web service should be satisfied with their participation rates in composite Web services Retention

20 WSCD Protocol

21 CN Protocol: WS Selection

22 Master WS Architecture

23 Slave WS Architecture

24 Protocol Interactions

25 Overview Context and Motivations Communities of Web Services: Definitions Web Services Communities: Engineering Argumentation between Web Services Conclusion and Future Work

26 Agents for WSs Agent 1 Agent 2 Negotiation Persuasion Cooperation Conflict solving … Conversations: Coherent sequences of utterances Reasoning Capabilities Reasoning Capabilities

27 The notion of argument: a pair An argument is a pair (P, c) where P is a set of beliefs and c is a formula, such that: i) P is consistent, ii) P c Argumentation

28 Argumentation is a dialectical process Attack relation: binary relation between arguments Argumentation Dynamics

29 Community Management Operations Argumentative Agent Framework Dialogue game protocols: specification, implementation, and verification Global View Argumentation-based Framework for Communities of WSs Communication, Negotiation and Persuasion between WSs

30 New Architecture of WSs Communities

31 Dialogue Games Abstract structures that can be composed: Sequencing: Embedding: Parallelization: Decision making process Computational analysis Game 1 Game 2, Game1 Game 2 …… Game 1 Game 2 //

32 Specification of Dialogue Games A persuasion/negotiation protocol Specification language Entry game Exit conditions (Termination) Chaining games Action_Ag 1 Action_Ag 2 Cond

33 Entry Game

34 Defense Game

35 Attack Game

36 PNAWS Protocol PNAWS: Persuasion/Negotiation for Agent-based Web Services protocol BNF grammar

37 Protocol Dynamics Defense game Attack game Justification game t1t1 t2t2 t3t3 t4t4 Acceptance Challenge game Acceptance Challenge game Attack game Refusal Termination Entry game t0t0

38 For any dialogue games, the PNAWS protocol always terminates Recursive definition The same move is prohibited The content of communicative acts is finite Challenge and attack moves are finite The agent-based WS’s knowledge bases is finite Termination Proof

39 Effect of using argumentative agents on QoS Reasoning about small knowledge base is efficient Polynomial time algorithms when using Horn clauses Complexity

40 (1) XML used for request and response specification between users and WSs and also between master WS and slave WSs (2) JDK 1.4 used for operation processing, (3) Jack for argumentative agents and dialogue games (4) Eclipse 3.1 as an integrated development environment Implementation

41 Implementation: System Architecture

42

43 Conclusion From WSs to Communities of WSs Specification and development of an argumentation-based framework for communities of WSs Advantages: Autonomous and flexible WSs and composite WSs Intelligent and dynamic WSs

44 Future Work Specifying other protocols using the developed framework Defining operational and denotational semantics for these protocols Verifying these protocols by model checking Developing security policies for the communities

45 Collaborators Zakaria Maamar: Zayed University, Dubai, United Arab Emirates Djamal Benslimane: Claude Bernard Lyon 1 University, Lyon, France Philippe Thiran: University of Namur, Namur, Belgium Sattanathan Subramanian: University of Namur, Namur, Belgium Oxford Brookes University, Oxford, UKMuhammad Younas: Oxford Brookes University, Oxford, UK

A Framework to Engineer Communities of Web Services Jamal Bentahar Concordia University (Montreal, Canada) Royal Holloway, University of London July 09, 2007