Analyzing BPEL4Chor: Verification and Participant Synthesis

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

BPEL4Chor Analyzing BPEL4Chor - Veriﬁcation and Partner Synthesis   extension to describe choreographies behaviors topology grounding 3

An Example Choreography Analyzing BPEL4Chor - Veriﬁcation and Partner Synthesis   taken from the paper introducing BPEL4Chor   one traveler, one agency, several airline instances 4

Analyzing BPEL4Chor - Veriﬁcation and Partner Synthesis 5

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

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

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

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

Analysis Result Analyzing BPEL4Chor - Veriﬁcation and Partner Synthesis   Choreography can deadlock!   each participant is correct (controllable, sound…)   deadlock very subtle! 10

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

Analyzing BPEL4Chor - Veriﬁcation and Partner Synthesis 12

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

Translation Analyzing BPEL4Chor - Veriﬁcation and Partner Synthesis   incomplete choreography is translated with BPEL2oWFN   translationyields an open workﬂow net with interface to missing participant 14

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

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

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

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

Analyzing BPEL4Chor: Verification and Participant Synthesis

by Universität Rostock

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