Realizabilityof Interaction Models
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  • 1. Realizability of Interaction Models Gero Decker ZEUS Workshop, Stuttgart 3 Mar 2009
  • 2. Agenda
      • Why use the interaction modeling style (rather than the interconnection modeling style)?
      • When are choreographies realizable , i.e. there exist participants that collectively realize the specified behavior?
      • What impact do branching structures have on realizability checking?
  • 3. Process Choreographies
      • Inter-organizational integration requires interaction contracts
        • Defined document structures / message types
        • Defined interaction behavior: constraints and obligations
    • “ A choreography defines the sequence and conditions under which multiple cooperating independent agents exchange messages in order to perform a task to achieve a goal state.” [W3C Glossary]
  • 4. Choreography Modeling
  • 5. Two Modeling Styles
      • Local ordering constraints
      • Distinction between control flow and message flow
      • MSC, BPMN
      • BPEL4Chor
      • Global ordering constraints
      • Interactions as atomic building blocks
      • UML Comm. Diagrams
      • BPSS, WS-CDL
      • Let’s Dance, iBPMN
    Interconnection Models Interaction Models
  • 6. Interconnection Models incompatible loops incompatible branching structures incompatible sequence flow abstraction level = messages
  • 7. Interaction Models atomic interactions decision ownership global control flow dependencies complex interactions global loops
  • 8. Interaction Petri Nets
  • 9. Interaction Petri Nets Customer Manufacturer Reseller Payment Org
  • 10. Realizability
  • 11. Realizability – Two Dimensions
      • Communication model
        • Synchronous (blocking send vs. failing)
        • Asynchronous (FIFO queue vs. standard buffer)
      • “ Similarity” of behavior
        • Complete behavior
        • Subset of behavior (proper termination vs. reachability constraints)
        • Equivalence notion (trace vs. bi-simulation vs. …)
  • 12. Realizability – Existing Work
      • Fu, Bultan & Su: Realizability (2004)
        • Projection: remove transitions + minimal deterministic automaton
        • Asynchronous, complete behavior (trace equivalence)
      • Decker & Weske: Local Enforceability (2007)
        • Projection: remove transitions + keep branching structure
        • Synchronous, subset of behavior (pattern-based + “blocked” transitions)
      • Decker, Barros, Kraft & Lohmann: Desynchronizability (2008)
        • Requires realizability for the synchronous case
        • Weak termination for the asynchronous case
  • 13. Fu, Bultan & Su: Realizability (2004) Traces = { [(A, τ ,A),(A,x,B),(B,y,C)], [(A, τ ,A),(A,x,B)]} Traces = { [(A, τ ,A),(A,x,B),(B,y,C)], [(A, τ ,A),(A,x,B)]}
  • 14. Now: Focus on Branching Structures
  • 15. Role Projection: Preserving Branching Structures
  • 16. Role Projection: Preserving Branching Structures
  • 17. Role Projection: Preserving Branching Structures
  • 18. Open Issue: Proofs
      • Define Full Realizability : There exist role behavior models the composition of which are bi-similar to the choreography
      • Theorem: A choreography is fully realizable if and only if the composition of the role projections is bi-similar to the choreography
      • Proof (idea): Show that the role behavior models must look exactly like they look if their composition is to be bi-similar
  • 19. Open Issue: Subset of Behavior
      • If a choreography is not fully realizable then
        • Remove transitions from the composition that are not allowed by to the choreography
        •  Imply which transitions in the role behavior models must be removed to achieve this removal in the composition
        • Try to find (reduced) role behavior models the composition of which shows a valid subset of the behavior of the choreography
  • 20. Conclusion
      • Interaction modeling imposes challenge of realizability
      • Different flavors of realizability
        • Communication model / similarity of behavior
      • Role projection as “best guess” for local behavior
      • Branching structures important if local choices to be considered
      • Role projection must reflect branching structures
      • Unifying theory still missing  Niels?
  • 21. Questions?
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