Bridging the gap between Interaction and ProcessOriented Choreographies

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Bridging the gap between Interaction- and
Process-Oriented Choreographies

• Talk by Ivan Lanese
• Joint work with Claudio Guidi,
• Fabrizio Montesi and Gianluigi Zavattaro
• University of Bologna, Bologna, Italy

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Roadmap

• IOCs and POCs
• Different interpretations for IOC
• Connectedness conditions
• Bisimilarity results
• Conclusions

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Roadmap

• IOCs and POCs
• Different interpretations for IOC
• Connectedness conditions
• Bisimilarity results
• Conclusions

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Choreography

• Choreography aims at describing the interactions
  among many participants
• Interaction-Oriented Choreography (IOC) obtained
  by composing basic interactions using
  composition operators
• WS-CDL
• Process-Oriented Choreography (POC) obtained as
  the parallel composition of the behavior of
  different roles
• BPEL4CHOR, natural extension of orchestration
  language BPEL

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From design to implementation

• IOCs are more easy to understand and to write
• Good tool for design
• POCs are more easily implementable
• We want to translate automatically a IOC into a
  POC
• We project the IOC on the different roles

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Which is the behavioral relation
between a IOC and the projected POC?
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Interaction-oriented Choreography

• Allows to describe interactions from a global
  point of view

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Process-oriented Choreography

• Allows to compose the behaviours of different
  roles
• Behaviours are based on input/output on
  operations
• We give two semantics to POCs a synchronous and
  an asynchronous one

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Asynchronous behaviours
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Composing behaviours

• In the synchronous semantics the output is
  immediately propagated and matched with the input

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Roadmap

• IOCs and POCs
• Different interpretations for IOC
• Connectedness conditions
• Bisimilarity results
• Conclusions

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Our aim

• Given a IOC we want to project it onto roles to
  get a POC exhibiting the corresponding behaviors
• The projection is an homomorphism but for
• We look for connectedness conditions ensuring
  that such a projection behaves well
• The conditions and the meaning of behaves well
  depend on the interpretation of the IOC

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What means?

• Consider the simple IOC
• In the synchronous case the (atomic) interaction
  between a and b should occur before the (atomic)
  interaction between c and d
• In the asynchronous case there are different
  alternatives
• Sender the sending at a should occur before the
  sending at c
• Receive the receive at b should occur before the
  receive at d
• Sender-receive both of the above
• Disjoint both the sending at a and the receive
  at b should occur before both the sending at c
  and the receive at d

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A partial order
Disjoint
Sender
Receiver
Strincter constraints on IOC
Sender - receiver
Stronger relation on behaviors
Synchronous
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Roadmap

• IOCs and POCs
• Different interpretations for IOC
• Connectedness conditions
• Bisimilarity results
• Conclusions

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Connectedness for sequence

• Ensures the correctness of sequential composition
• Synchronous a,b n c,d ? Ø
• Sender ac or bc
• Receiver bc or bd
• Disjoint bc
• The conditions can be generalized to ensure the
  connectedness of

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Example

• Consider
• The projection is
• The POC behaves well for synchronous and sender
  semantics
• The POC is not connected for receiver or disjoint
  semantics

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Points of choice
?

• Ensures the correctness of choice
• Synchronous
• The same role should occur in each initial
  transitions
• The roles in the two components should be the
  same
• Asynchronous
• The sender should be the same
• The roles in the two components should be the
  same

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Points of choice example

• If we drop the condition on roles
• In the projection
• Interaction on O3 is enabled

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Causality-safety

• Using many times the same operation may cause
  problems
• For instance a may interact with d

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Causality-safety

• We define a causality relation between events of
  the projected POC
• e1 lt e2 if e2 becomes enabled after e1 has been
  performed
• the exact definition depends on whether the
  semantics is synchronous or asynchronous
• We require causality dependencies between events
  on the same operation
• At most one of them can be enabled at the time
• No interference

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Roadmap

• IOCs and POCs
• Different interpretations for IOC
• Connectedness conditions
• Bisimilarity results
• Conclusions

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Bisimilarity

• We characterize the behavioral relation between a
  IOC and the projected POC using bisimilarity
• Synchronous bisimilarity IOC transitions are
  matched by synchronous POC transitions
• Sender bisimilarity IOC transitions are matched
  by POC sends, POC receives are abstracted away
• weak w.r.t. POC receive transitions
• Receiver bisimilarity IOC transitions are
  matched by POC receives, POC sends are abstracted
  away
• weak w.r.t. POC send transitions
• Disjoint bisimilarity a IOC transition is
  matched by subsequent send and receive POC
  transitions

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Main result

• If a IOC satisfies all the connectedness
  conditions for the synchronous/sender/receiver/dis
  joint semantics then it is synchronous/sender/rece
  iver/disjoint bisimilar to its projection

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Receive bisimulation example
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Receive bisimulation example
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Roadmap

• IOCs and POCs
• Different interpretations for IOC
• Connectedness conditions
• Bisimilarity results
• Conclusions

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Extensions

• Internal located actions, recursion and hiding
  can be added to the language
• Value passing can be added
• A role should own the value to be sent
• Values can be used to transform nondetermistic
  choice into deterministic

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Bisimulation

• Bisimulations and simulations can be defined both
  for IOCs and for POCs
• IOC-POC bisimulation is compatible with those
  (bi)simulations
• The projections of two (bi)similar IOCs are
  bisimilar
• One can refine a IOC (e.g., adding auxiliary
  interactions) and derive a refined POC
• Refinement can solve connectedness problems
• Hiding is necessary to have more powerful
  refinements

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Conclusion

• We started from the basic question which is the
  meaning of a IOC?
• We derived different possible interpretations
  according to the choice of synchronous/asynchronou
  s semantics and to the observable events
• For each possibility
• We found suitable syntactic conditions ensuring a
  correct projection
• We characterize the behavioral relation between
  IOC and POC as a suitable bisimulation relation

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Related work

• Carbone, Honda, Yoshida, Structured
  communication-centred programming for web
  services, ESOP 07
• Honda, Yoshida, Carbone, Multiparty asynchronous
  session types, POPL 08
• Bravetti, Zavattaro, Towards a unifying theory
  for choreography conformance and contract
  compliance, SC 07
• Busi et al., Choreography and orchestration
  conformance for system design, COORDINATION 06
• Li, Zhu, Pu, Conformance validation between
  choreography and orchestration, TASE 07

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Future work

• Complete the analysis on a more complex language
• Recursion/iteration
• Data
• Hiding
• Exceptions
• Looking at more complex projection functions
• Should allow to relax the connectedness
  conditions
• Study the possibility of refinement

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Thanks!
Questions?
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