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A-Priori Verification of Web Services with Abduction

A-Priori Verification of Web Services with Abduction. Marco Alberti 1 Federico Chesani 2 Marco Gavanelli 1 Evelina Lamma 1 Paola Mello 2 Marco Montali 2. 1 ENDIF, Università di Ferrara 2 DEIS, Università di Bologna. Motivation: Service Oriented Computing. Web services:

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A-Priori Verification of Web Services with Abduction

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  1. A-Priori Verification of Web Services with Abduction Marco Alberti1 Federico Chesani2 Marco Gavanelli1 Evelina Lamma1 Paola Mello2 Marco Montali2 1 ENDIF, Università di Ferrara 2 DEIS, Università di Bologna

  2. Motivation: Service Oriented Computing • Web services: • Defined by their behavioural interface • Simple stand-alone applications, or • Potential components of complex applications, by • Composition of web services: • As specified by a choreography • Will the web services comply to the choreography? A-Priori Verification of Web Services with Abduction

  3. Choreographies vs. MAS protocols • Similarities (Baldoni et al., LNCS 3670): • Both define rules for collaboration among peers • Both express dependencies and constraints in interactions • Both abstract away from internals, focusing on interface • Wide literature on MAS protocol verification • Approach: apply MAS techniques to SOC verification A-Priori Verification of Web Services with Abduction

  4. In this talk: The AlLoWS framework • Abductive Logic Web-service Specification • Language to specify choreographies and web service interfaces (originally: interaction protocols and reactive agents), with an abductive semantics • Definition of conformance of a web service to a choreography • Abductive proof procedures to verify conformance A-Priori Verification of Web Services with Abduction

  5. Representation of interactions Interaction as exchange of messages. • Messages format: • mx(Sender, Receiver, Content) • Events: actual message exchanges • H(Message[,Time]) • Expectations: desired message exchanges • E(Event[,Time]) A-Priori Verification of Web Services with Abduction

  6. Choreography Specification • Abductive triple <KBchor,εchor,ICchor> • ε: abducible signatures (events H and expectations Echor) • Choreography Knowledge Base: logic program with expectations in clause bodies • Choreography Integrity Constraints: implications relating events and expectations A-Priori Verification of Web Services with Abduction

  7. Choreography example KBchor • deadline(10). ICchor • H(m1(X,Y),T1) /\ deadline(Td) → Echor(m2(Y,X),T2) /\ T2< T1 + Td \/ Echor(m3(Y,X),T2) /\ T2< T1 + Td A-Priori Verification of Web Services with Abduction

  8. Web Service specification • Abductive triple <KBws,εws,ICws> • ε: abducible signatures (events H and expectations Ews) • Web service Knowledge Base: logic program with expectations in clause bodies • Web service Integrity Constraints: implications relating events and expectations A-Priori Verification of Web Services with Abduction

  9. Conformance • Our idea of conformance: a web service will comply to a choreography,provided that its peers comply too. • Feeble conformance: all expected events happen. • Strong conformance: all happened events are expected. A-Priori Verification of Web Services with Abduction

  10. Possible interaction • A pair (HAP, EXP) that, together with the KB, entails the following: • a Goal (usually defines a needed event) • The integrity constraints • The web service being discussed follows its own expectations about itself • The other peers follow the choreography expectations about themselves A-Priori Verification of Web Services with Abduction

  11. Feeble conformance A possible history HAP is feeble conformant if there exists EXP that, together with joined KBs, entails: • A goal • The integrity constraints (ICchor U ICws) • Ews(X)  H(X) • Echor(X)  H(X) • <HAP,EXP> is a feeble conformant interaction if EXP is minimal w.r.t set inclusion • A web service is feeble conformant if all the possible histories are feeble conformant A-Priori Verification of Web Services with Abduction

  12. Strong conformance A feeble conformant interaction <HAP,EXP> is also strong conformant if it entails the following: • H(mx(ws,R,C))  Echor(mx(ws,R,C)) • H(mx(S,ws,C))  Ews(mx(S,ws,C)) A web service is strong conformant if all possible histories are strong conformant. A-Priori Verification of Web Services with Abduction

  13. The SCIFF abductive proof procedure • Derived from Fung and Kowalski’s IFF • Originally applied to compliance verification in MAS • Properties: • Termination for acyclic programs • Soundness • Completeness • Generative version: g-SCIFF (events are abducible) • Applied to verification of protocol properties A-Priori Verification of Web Services with Abduction

  14. Conformance verification SCIFF Feeble Conformance Are all events expected? g-SCIFF SCIFF /\ Possible Interaction HAP,EXP SCIFF Is HAP feeble conformant? Strong Conformance A-Priori Verification of Web Services with Abduction

  15. Example: more capabilities • Choreography • H(m1(ws,X,C))→Echor(m2(X,ws,D)) • Web service • H(m1(ws,X,C)) →Ews(m2(X,ws,D)) \/ Ews(m3(X,ws,D)) • Result: feeble and strong conformant A-Priori Verification of Web Services with Abduction

  16. Example: Missing Capability • Choreography • H(m1(ws,X,C)) → Echor(m2(X,ws,D)) \/ Echor(m3(X,ws,D)) • Web service • H(m1(ws,X,C)) → Ews(m2(X,ws,D)) • Result: not feeble conformant • Counterexample: HAP = {H(m1(ws,a,c)),H(m3(a,ws,d))} A-Priori Verification of Web Services with Abduction

  17. Example: Wrong reply • Choreography • H(m1(X,ws,C)) → Ews(m2(ws,X,D)) \/ Ews(m3(ws,X,D)) • Web service • H(m1(X,ws,C)) → Echor(m2(ws,X,D)) • Result: non conformant • Counterexample HAP = {H(m1(a,ws,c)),H(m3(ws,a,d))} A-Priori Verification of Web Services with Abduction

  18. Example: Predefined answer • Choreography • H(m1(X,ws,C)) → Echor(m2(ws,X,D)) \/ Echor(m3(ws,X,D)) • Web service • H(m1(X,ws,C)) → Ews(m2(ws,X,D)) • Result: feeble and strong conformant A-Priori Verification of Web Services with Abduction

  19. Ongoing work • Is a uniform language good w.r.t expressiveness? • Automatic translation from graphical notations • Experimentation and (performance) comparison with other frameworks A-Priori Verification of Web Services with Abduction

  20. A-Priori Verification of Web Services with Abduction Marco Alberti1 Federico Chesani2 Marco Gavanelli1 Evelina Lamma1 Paola Mello2 Marco Montali2 Thank You! 1 ENDIF, Università di Ferrara 2 DEIS, Università di Bologna

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