Analyzing BPEL4Chor: Verification and Participant Synthesis
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The document discusses the analysis and verification of BPEL4Chor, which is an extension for describing service choreographies. It emphasizes the automated analysis of BPEL processes, the translation of BPEL4Chor into Petri nets, and the synthesis of missing participant descriptions to ensure deadlock-free choreographies. Key findings include the identification of potential subtle deadlock situations and the conclusion that BPEL4Chor choreographies can be completed automatically using a proposed toolchain.
Analyzing BPEL4Chor: Verification and Participant Synthesis
- 2. BPEL Analyzing BPEL4Chor - Verification and Partner Synthesis designed to describe a service orchestration … respectively a single service invoked services’ behaviors are not described BPEL processes can be automatically analyzed (BPM 2006; project Tools4BPEL) 2
- 3. BPEL4Chor Analyzing BPEL4Chor - Verification and Partner Synthesis extension to describe choreographies behaviors topology grounding 3
- 4. An Example Choreography Analyzing BPEL4Chor - Verification and Partner Synthesis taken from the paper introducing BPEL4Chor one traveler, one agency, several airline instances 4
- 5. Analyzing BPEL4Chor - Verification and Partner Synthesis 5
- 6. Analyzing BPEL4Chor Choreographies Analyzing BPEL4Chor - Verification and Partner Synthesis “Classical” properties: deadlock-freedom, livelock-freedom, no dead activities (a.k.a. Soundness) Messages: Does there exist a state in which more than one message is pending on a communication channel? What is the minimal/maximal number of messages to be sent to reach a final state? Behavior: Will a participant always receive an answer? Can a participant enforce the execution of an activity? 6
- 7. Translating BPEL4Chor into a Petri Net Analyzing BPEL4Chor - Verification and Partner Synthesis Extend compiler BPEL2oWFN BPEL2oWFN Static Analysis BPEL processes Translation Instantiation Composition Structural Reduction Petri net topology BPEL4Chor requires instantiation and composition 7
- 8. Instantiation Analyzing BPEL4Chor - Verification and Partner Synthesis … example for two airline instances t1 … trip <receive wsu:id="ReceiveTripOrder" /> price.1 <forEach wsu:id="fe_RequestPrice„ t2 t3 price.2 parallel="yes"> <scope> quote.1 <sequence> <invoke wsu:id="RequestPrice" /> t4 t5 quote.2 <receive wsu:id="ReceiveQuote" /> </sequence> </scope> t6 </forEach> order.1 <opaqueActivity name="SelectAirline" /> <invoke wsu:id="OrderTickets" /> t7 t8 order.2 … … 8
- 9. Composition Analyzing BPEL4Chor - Verification and Partner Synthesis each service is translated into an open workflow net with an interface open workflow nets can be composed resulting net has no interface (standard Petri net) 9
- 10. Analysis Result Analyzing BPEL4Chor - Verification and Partner Synthesis Choreography can deadlock! each participant is correct (controllable, sound…) deadlock very subtle! 10
- 11. Case Study airline instances Analyzing BPEL4Chor - Verification and Partner Synthesis 1 5 10 100 1000 places 20 63 113 1013 10013 transitions 10 41 76 706 7006 states 14 3483 9806583 exponential states 14 561 378096 growth states 11 86 261 18061 1752867 states 11 30 50 410 4010 complete/unreduced linear symmetry reduction growth partial order reduction symmetry reduction and partial order reduction out of memory (>2 GB) 11
- 12. Analyzing BPEL4Chor - Verification and Partner Synthesis 12
- 13. Partner Synthesis Analyzing BPEL4Chor - Verification and Partner Synthesis new setting: design phase of choreography one participant description is missing goal: synthesize missing participant description 13
- 14. Translation Analyzing BPEL4Chor - Verification and Partner Synthesis incomplete choreography is translated with BPEL2oWFN translationyields an open workflow net with interface to missing participant 14
- 15. Partner Synthesis (1) Analyzing BPEL4Chor - Verification and Partner Synthesis Fiona Partner synthesis open workflow net open workflow net (incomplete choreography) (synthesized participant) Fiona can synthesize a partner if one exists partner is correct by design partner’s behavior is based on communication no internal behavior is synthesized order of messages is as relaxed as possible 15
- 16. Partner Synthesis (2) Analyzing BPEL4Chor - Verification and Partner Synthesis oWFN2BPEL Retranslation open workflow net abstract BPEL process (synthesized participant) (synthesized participant) partner’s behavior can be described using BPEL derived BPEL process is abstract has to be refined to an executable process 16
- 17. Limits of the Partner Synthesis Analyzing BPEL4Chor - Verification and Partner Synthesis can only synthesize one partner: If more than one airline instance is synthesized, the generated partners explicitly synchronize. airline instances would communicate timeouts: one instance would be forced to wait for a message can be a starting point for diagnosis causalitiesof messages might be ignored order and invoice messages might be concurrent can be fixed using constraints 17
- 18. Take-home Points Analyzing BPEL4Chor - Verification and Partner Synthesis BPEL4Chor choreographies can be analyzed … to find very subtle errors … even with thousands of participants … automatically using the proposed tool chain BPEL4Chor choreographies can be completed … by synthesizing the missing participant … to guarantee a deadlock-free choreography ... automatically using the proposed tool chain Thank you very much! 18