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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

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

motivation service oriented computing
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

choreographies vs mas protocols
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

in this talk the a l lows framework
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

representation of interactions
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

choreography specification
Choreography Specification
  • Abductive triple
  • 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

choreography example
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

web service specification
Web Service specification
  • Abductive triple
  • 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

conformance
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

possible interaction
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

feeble conformance
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)
  • 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

strong conformance
Strong conformance

A feeble conformant interaction 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

the s ciff abductive proof procedure
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

conformance verification
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

example more capabilities
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

example missing capability
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

example wrong reply
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

example predefined answer
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

ongoing work
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

a priori verification of web services with abduction1

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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