Distributed Agent Architecture and Case-Based Approach for Information System Integration

1. A distributed agent architectureand case-based approachfor information system integration Computer Science Institute University of Ancona Loris Penserini (pense@inform.unian.it) In collaboration with: Maurizio Panti (panti@inform.unian.it) Luca Spalazzi (spalazzi@inform.unian.it) (these slides are available at: http://www.cs.toronto.edu/~mkolp/tropos/) Computer Science Institute - University of Ancona

2. Motivation In a network environment the principal problems of Information System Integration are: - distribution: the needing of sharing sources between LANs and/or WANs - dynamism: new sources can be inserted or deleted, the schemas can be modified and so on - heterogeneity: discrepancies in physical, logical, and conceptual levels Computer Science Institute - University of Ancona

3. Work Purpose - to use an Agent Platform to face the distribution - to solve dynamic problems by a Distributed CBR approach - to adopt a Mediator architecture to face the heterogeneity - to evaluate both the efficacy and the efficiency of the Mediator cooperation strategies by a prototype implementation Computer Science Institute - University of Ancona

4. * Agent Platform architecture FIPA compliant * Mediator agent that uses a Distributed CBR Software * Mediator prototype and Cooperation Strategies Case Memory2 Agent Case Memory1 Mediator1 Mediator2 Wrapper1 Wrapper2 Agent Management System Directory Facilitator db1 db2 Agent Communication Channel Summary Computer Science Institute - University of Ancona

5. JEAP&FIPA FIPA Reference Model Agent Platform (AP) architecture. AP 1 AP 2 ? ? DF DF AMS AMS ACC ACC Agents Agents IIOP The network IIOP IIOP ? ACC AMS DF Agents AP 3 Computer Science Institute - University of Ancona

6. JEAP&FIPA Communication Protocol FIPA Specification: FIPA defines two types of communication: • Intra-platform No constraints • Inter-platform Internet Inter-ORB Protocol CORBA allows several mechanisms in order to locate distribute objects, which are incompatible each other, but FIPA does not specify which one must be used. Computer Science Institute - University of Ancona

7. JEAP&FIPA Communication Protocol AP prototype implementation: Intra-platform protocol: IIOP • IIOP is a well known standard. • Code Portability. • ACC is simpler. Computer Science Institute - University of Ancona

8. JEAP&FIPA Communication Protocol AP prototype implementation: CORBA mechanisms • Interoperable Object Reference (IOR) • Transient Name Service (TNS) Wide compatibility with other FIPA compliant platforms. Computer Science Institute - University of Ancona

9. JEAP&FIPA Agent Communication Channel (ACC) and Agent Management System (AMS) FIPA Specification: ACC and AMS strictly interact each other. ACC supports two kinds of request: • implicit ACC request; • explicit ACC request (forward action); Computer Science Institute - University of Ancona

10. JEAP&FIPA ACC and AMS Example: A second source of overload is the task that ACC must do for explicit requests: (request :sender agent_i@iiop://192.168.1.1:800/acc :receiver acc@iiop://192.168.1.1:800/acc :language sl0 :ontology fipa-agent-management :protocol fipa-request :content (action acc@iiop://192.168.1.1:800/acc (forward (MESSAGE) )) :reply-with 0) Computer Science Institute - University of Ancona

11. JEAP&FIPA ACC and AMS Agent_i Agent_j ACC AMS 1: request for Agent_j 2: request 3: agree 4: authenticate 5: inform 6: request from Agent_i 7: agree for Agent_i 8: request 9: agree 10: authenticate 11: inform 12: agree from Agent_j 13: inform done for Agent_i 14: request 15: agree 16: authenticate 17: inform 18: inform done from Agent_j Computer Science Institute - University of Ancona

12. JEAP&FIPA ACC and AMS AP prototype implementation: ACC and AMS are realised as a single agent: • It removes the interaction between ACC and AMS. • It does not decrease fault-tolerance capability of the platform. • It is still FIPA compliant. Computer Science Institute - University of Ancona

13. JEAP&FIPA ACC and AMS AP prototype implementation: We only use implicit requests. • It reduces the overload for the ACC. • It is still FIPA compliant. Computer Science Institute - University of Ancona

14. JEAP&FIPA Directory Facilitator (DF) FIPA Specification: The DF provides a yellow-pages service. The agents registered at the DF are classified by means of service-type and service-name. A Domain is the set of all the agents registered at the DF. The Agent Universe is the union of all the domains. Each Agent Platform must have at least one DF (the default DF). Computer Science Institute - University of Ancona

15. JEAP&FIPA FIPA Platforms and Domains Computer Science Institute - University of Ancona

16. JEAP&FIPA Directory Facilitator (DF) AP prototype implementation: Specification are not clear on what default DF can contain and which kind of service-name it must use. default DF Service Type Level FIPA-DF FIPA–ACC FIPA – AMS Service Name Level Airport Railway Agent DF Level (GUID) DF_i DF_j DF_k … Logic structure of the default DF. Computer Science Institute - University of Ancona

17. JEAP&FIPA Agent Platform 1:Search for a domain Agent_i DF Default 2:Answer with DF_j address 3:Search for an agent 5:Invoke the service 6:Results 4:Answer with agent address (Agent_k) DF_j Agent_k Directory Facilitator (DF) AP prototype implementation: example A possible situation in which Agent_i would like to use a service that can perform the Wrapper_i, but at the begin Agent_i doesn’t know that. Computer Science Institute - University of Ancona

18. JEAP&FIPA Some Remarks on FIPA FIPA is an effective solution to agent cooperation in heterogeneous and distributed environments. Nevertheless FIPA specification are not clear: • Communication protocols: intra-platform and inter-platform; • ACC and AMS: they have a strictly interaction and ACC is overburdened by the forward action; • Default DF: its role and organisation are not clear. Computer Science Institute - University of Ancona

19. DCBR approach Project Overview Computer Science Institute - University of Ancona

20. CBR approach Query Representation: Case Memory Example: Computer Science Institute - University of Ancona

21. CBR approach Local Query Rewriting: Terminology The problems (queries, Q) are classifies according to subsumption relation. In particularly, in this work, Q is decomposed and then classified. For example: Computer Science Institute - University of Ancona

22. CBR approach Local Query Rewriting Query Evaluation: the Mediator sends a decomposition of Q to the related information source and wait for their answers. Local Failure in Query Reuse: the Mediator is not able to rewrite Q since its case memory contains no past cases that can be used to do it. For example, it is the first time that the consumer formulates such a query, i.e., the consumer has a new information need. Local Failure in Query Evaluation: the Mediator sends a rewritten query to related sources and receives at least an empty answer. This means that the case memory of the mediator is not updated (an information source has been removed from system or changed its schema). Computer Science Institute - University of Ancona

23. DCBR approach Distributed Query Rewriting Principal Cooperation Strategies: Partners Queries Answers Mediators Sources Original Rewritten Rewritten Data all, the newer, the older, ... the whole query, its components, ... Computer Science Institute - University of Ancona

24. DCBR approach Distributed Query Rewriting A first strategy: the Mediator cooperates with other mediators, send them the original query, and asks for receiving the rewritten query. First consideration Theorem. Let M, N be two mediators such that M interacts with N when M fails. Let Cn(M) be the case memory of M after n interactions with N. Let Cn(N) be the case memory of N such that it does not change while N interacts with M. Then redundancy Computer Science Institute - University of Ancona

25. DCBR approach Distributed Query Rewriting A first strategy: the Mediator cooperates with other mediators, send them the original query, and asks for receiving the rewritten query. Second consideration Theorem. Let be n information sources. Let V be a view of . Let M, N be two mediators such that M interacts with N when M fails. Let Cn(M) be the mediated schema of M after n interactions with N. Then Computer Science Institute - University of Ancona

26. DCBR approach Distributed Query Rewriting A second strategy: the Mediator cooperates with information sources, sends them the original query, and receives the rewritten query. Theorem. Let be n information sources. Let V be a view of . V is represented as a case memory that does not change. Let M be a Mediator such that M interacts with when it fails. Let Cn(M) be the case memory of M after n interactions with . Then Computer Science Institute - University of Ancona

27. DCBR approach Some Considerations Notation Sol (Q) : the solution of Q (problem) respect the source S --> rewritten I (Sol (Q)) : the interpretation of the solution of Q both respect the source S --> data S S S Computer Science Institute - University of Ancona

28. Mediator Prototype Mediator Prototype - Its language is a restrict set of Sequel Query Language - It implements a wide set of cooperation strategies - It collaborates with other mediators and ‘simple’ wrappers - Its Solution-Analysing and the Case-Memory Updating phases are still user driven Computer Science Institute - University of Ancona

29. Mediator Prototype PROB:select EmployeeInfo from Employee SOL:"select EmployeeName from Employees@wrapper1@ iiop:// 129.100.27.30:900/acc" and "select EmployeeAddr from Address@wrapper2@iiop://193.205.128.40:1000/acc" Case Memory Organization Computer Science Institute - University of Ancona

30. Mediator Prototype Failure in Retrieval Different cases of failure during retrieval: - in reuse - in evaluation (partial or total) - by the user feedback Computer Science Institute - University of Ancona

31. Mediator Prototype Session Example failure in reuse Agent i Mediator Wrapper 1 Wrapper 2 1: solution requests to mediator 2: It checks in its knowledge ð OK Wrapper interrogation 3.1: request to wrapper 1 solve 4.1: 3.2: request to wrapper 1 solve 4.2: 3.3: request to wrapper 2 4.3: solve 5.1: data partial failure in evaluation 5.2: failure 5.3: data 6: Case Memory update 7.1: data user feedback 7.2: failure 7.3: data Computer Science Institute - University of Ancona

32. Mediator Prototype select EmployeeInfo from Employee Cooperation Strategies Computer Science Institute - University of Ancona

33. Mediator Prototype 1: request Mediator 1 Mediator 2 2: rewrite 3: data 2: data 3: data W1 W2 W3 Cooperation Example Computer Science Institute - University of Ancona

34. Mediator Prototype Strategies Evaluation The tests have evaluated, for each strategy, these kinds of problems : - knowledge growing - knowledge redundancy - response time - network overload Computer Science Institute - University of Ancona

35. Mediator Prototype Strategies Evaluation The principals tests consist in five general queries (problems) all performed on the following five different strategies: Strategy 1: a mediator (M) sends the original query (Q) to another mediator (N) and requests for a rewrite Strategy 2: M sends a decomposition of Q to N and requests for a rewrite Strategy 3: M sends to N only the rewrited components of Q that it cannot solve and asks for the data Strategy 4: M directly sends a decomposition of Q to the wrappers and asks them for the data Strategy 5: M directly sends only the rewrited components of Q to the wrappers and asks for the data Computer Science Institute - University of Ancona

36. Mediator Prototype Strategies Evaluation: Results Computer Science Institute - University of Ancona

37. Mediator Prototype Strategies Evaluation: Results Computer Science Institute - University of Ancona

38. Mediator Prototype Strategies Evaluation: Results Steps: principal phases of a communication (without any FIPA protocols) Service Messages: they do not contain data (query responses) inside otherwise they should be considered ‘Data Messages’ Small/Big Messages: it is another possible type of messages subdivision based on the content of a FIPA message (e.g. an ‘agree’ message is considered ‘small’, whereas an ‘inform’ messages is big, and so on) Computer Science Institute - University of Ancona

39. Future Development - The designing and developing of a Mediator agent that uses a CBR engine based on DL - The designing of protocols that automatically choice the best strategy in response to a particular failure - To consider other useful cooperation strategies - To apply this architecture in a real case of interest to test its capacity (e.g. some kind of web applications) Computer Science Institute - University of Ancona

40. References - M. Panti, L. Penserini, L. Spalazzi, S. Valenti, "A FIPA Compliant Agent Platform for Federated Information Systems", International Journal of Computer & Information Science, R. Y. Lee and H. Fouchal (eds), ACIS, 2000. - C. Cioffi, M. Panti, L. Penserini, L. Spalazzi, E. Tonucci, S. Valenti, ``An Agent-Based Platform for Federated Information Systems: Some Design Issues'', in Proc. of the International Conference on Software Engineering Applied to Networking and Parallel/Distributed Computing (SNPD '00), Reims, France, May 18-21, 2000. - M. Panti, L. Penserini, L. Spalazzi, ``A Critical Discussion about an Agent Platform based on FIPA Specification'', in Atti dell'Ottavo Convegno Nazionale su Sistemi Evoluti per Basi di Dati (SEBD 2000), L'Aquila Italia, 26-28 Giugno 2000. - M. Panti, L. Spalazzi, A. Giretti, “A case-based approach to information integration”, In Proceedings of the 26th International Conference on Very Large Databases, Cairo, Egypt, 10–14 September 2000. - Foundation for Intelligent Physical Agents, Fipa 2000 Specification. Geneva, Switzerland, October 2000. Available at: http://www.fipa.org/ - E. Plaza, J. L. Arcos, and F. Martìn, “Cooperative Case-Based Reasoning”, In G. Weiss, editor, Distributed Artificial Intelligence meets Machine Learning, Lecture Notes in Artificial Intelligence, Berlin, 1997. Springer Verlag. - G. Wiederhold, “Mediators in the architectures of future information systems”, in IEEE Computer, vol. 25, N. 3, pp. 38--49, 1992. Computer Science Institute - University of Ancona