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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. Roadmap. IOCs and POCs Different interpretations for IOC Connectedness conditions

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Bridging the gap between interaction and process oriented choreographies

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


Roadmap

Roadmap

IOCs and POCs

Different interpretations for IOC

Connectedness conditions

Bisimilarity results

Conclusions


Roadmap1

Roadmap

IOCs and POCs

Different interpretations for IOC

Connectedness conditions

Bisimilarity results

Conclusions

3


Choreography

Choreography

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  • 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

4


From design to implementation

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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Bridging the gap between interaction and process oriented choreographies

Which is the behavioral relation

between a IOC and the projected POC?

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Interaction oriented choreography

Interaction-oriented Choreography

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Allows to describe interactions from a global point of view

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Process oriented choreography

Process-oriented Choreography

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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

Asynchronous behaviours

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Composing behaviours

Composing behaviours

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

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Roadmap2

Roadmap

IOCs and POCs

Different interpretations for IOC

Connectedness conditions

Bisimilarity results

Conclusions

11


Our aim

Our aim

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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

What ; means?

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  • 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

A partial order

Disjoint

Sender

Receiver

Strincter constraints

on IOC

Sender - receiver

Stronger relation

on behaviors

Synchronous

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Roadmap3

Roadmap

IOCs and POCs

Different interpretations for IOC

Connectedness conditions

Bisimilarity results

Conclusions

15


Connectedness for sequence

Connectedness for sequence

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Ensures the correctness of sequential composition

Synchronous: {a,b} ∩ {c,d} ≠ Ø

Sender: a=c or b=c

Receiver: b=c or b=d

Disjoint: b=c

The conditions can be generalized to ensure the connectedness of

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Example

Example

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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

Points of choice

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  • 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

Points of choice: example

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If we drop the condition on roles:

In the projection

Interaction on O3 is enabled

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Causality safety

Causality-safety

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Using many times the same operation may cause problems

For instance a may interact with d

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Causality safety1

Causality-safety

  • We define a causality relation between events of the projected POC

    • e1 < 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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Roadmap4

Roadmap

IOCs and POCs

Different interpretations for IOC

Connectedness conditions

Bisimilarity results

Conclusions

22


Bisimilarity

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

Main result

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

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Receive bisimulation example

Receive bisimulation example

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Receive bisimulation example1

Receive bisimulation example

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Roadmap5

Roadmap

IOCs and POCs

Different interpretations for IOC

Connectedness conditions

Bisimilarity results

Conclusions

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Extensions

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

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

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/asynchronous 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

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

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

32


Bridging the gap between interaction and process oriented choreographies

Thanks!

Questions?

33


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