Toward Design, Modelling and Analysis of Dynamic Workflow Reconfiguration: a Process Algebra Perspective
- 1. Toward Design, Modelling and analysis of Dynamic Workflow Reconfiguration A Process Algebra Perspective M. Mazzara, F. Abouized, N. Dragoni and A. Battacharyya WSFM’11 8 th International Workshop on Web Services and Formal Method 1/9/2011, Clermont-Ferrand, France
- 2. Contributors (Just) some of the most important people to thank for their research inputs over the last few years… Cliff Jones, Alexander Romanovsky, Paolo Missier, Vasa Curcin, Jeremy Bryans, Gudmund Grov, Massimo Strano, Michele Mazzucco, Kamarul Abdul Basit, Carl Gamble, Richard Payne, Mario Bravetti, Cosimo Laneve, Roberto Lucchi, Claudio Guidi, Ivan Lanese… Anirban Bhattacharyya - Newcastle University, UK John Fitzgerald - Newcastle University, UK Faisal Abouzaid - Ecole Polytechnique de Montreal, Canada Nicola Dragoni - Technical University of Denmark Mu Zhou - Technical University of Denmark Koji Hasebe, University of Tsukuba, Japan Juan Carlos Polanco Aguilar, University of Tsukuba, Japan
- 3. Introduction and open issues Requirements on formalisms and synopsis A novel formalism Workflow Reconfiguration Modelling/Verification Implementation Discussion Agenda
- 4. I describe the requirements a formalism for dynamic reconfiguration should meet I analyze well-known formalisms against these requirements and we make a synopsis I discover how just a few of these requirements are met by these formalisms I discuss how the “ideal formalism” should look like I explain why it is not possible to achieve this now I introduce a novel formalism which copes well I show working examples of this The “story” I am going to tell you…
- 5. Research on reconfiguration is vast Service reconfiguration is not extensively researched yet Computational models Formalisms Methods Tools Overlapping modes are relevant in the services context especially when high traffic is involved Research on reconfigurable systems
- 6. Overlapping Modes configuration 1 configuration 2 Case 1 configuration 2 configuration 1 dynamic reconfiguration transactions Case 2 configuration 2 configuration 1 normal transactions dynamic reconfiguration transactions interactions (functional/temporal) Case 3
- 7. Keeping an eye on the real world… “ Man has such a predilection for systems and abstract deductions that he is ready to distort the truth intentionally, he is ready to deny the evidence of his senses only to justify his logic” (Fyodor Dostoyevsky)
- 8. Performing an instantaneous mode change in a distributed system is unrealistic… global state at a specific instant might be undefined … and waiting for the reconfiguration to be performed is not always acceptable e.g. services with very high traffic … when making sensible assumptions
- 9. Vocabulary Location Layer Application Layer Objects Nodes Links Connected by Components Connectors Hosted on Channels
- 11. Formalisms for Dynamic Reconfiguration The ideal formalism is one able to model all the aspects of reconfiguration and to work for the analysis
- 12. Simple Harmonic Motion In the domain of continuous phenomena differential equations are the paradigm The differential equation for simple harmonic motion elegantly describes all the aspects in a single equation
- 13. The Ideal Formalism what is being changed the change the rules Simple Harmonic Motion
- 14. But… … the formal elegance and power of differential equations took just thousands of years to develop!
- 15. We cannot spend so long thinking!!!
- 17. Messages can include channel names Sending an address and expecting a reply to that address Output capability (MS Biztalk) received names used as subjects of outputs only Input capability ( -calculus) received names used as the subject of inputs as well Reconfiguration features in π- calculi π
- 18. Language Syntax Semantics Pragmatics/examples Interaction Synchronization/message passing Mobility/reconfigurability Foundational model
- 19. Web π ∞ syntax
- 20. Semantics “ There are no facts, only interpretations” (Friedrich Nietzsche)
- 22. Dynamic reconfiguration of an office workflow Order processing in a large/medium-sized organisation High traffic of order has to be processed Change of procedure (reconfiguration) Billing is performed before shipping Sequence instead concurrency Case study
- 23. BPMN design
- 24. π-calculus modeling Old region New region
- 25. web π ∞ modeling Elements involved In triggering the new region Elements of the old region
- 26. Abstractions Workunits and event handlers are used to model the reconfiguration in a smart way Workunits bound the identified regions (old and new) Event raising is exploited to trigger the change The floating law (structural congruence) allows asynchronous outputs in a workunit to freely escape the workunit itself
- 27. Requirements During (and after) the transition phase: The acceptability of an order should not be affected by the change in procedure All accepted orders must be billed and shipped, then archived All orders accepted after the change in procedure must be processed according to the new procedure
- 28. Verification Equational reasoning is inadequate for reconfiguration What we have: Requirements specified in pi-logic Model checking in HAL Problem with state explosion! What we need: PROMELA description of the workflow reconfiguration Requirements described in LTL SPIN for model checking
- 29. WS-BPEL Implementation: questions WS-BPEL has not been designed for dynamic reconfiguration has been used to encode WS-BPEL Reconfiguration has been shown to work with Can the basic mechanisms of the WS-BPEL recovery framework support dynamic reconfiguration ? Web π ∞ Web π ∞
- 30. WS-BPEL Implementation: principles Three basic principles have been followed: The regions to be reconfigured have to be represented by BPEL scope Each BPEL scope (i.e. region) will be associated with termination and event handlers An event triggers the new configuration terminating the old one
- 31. Discussion of the case study
- 32. Workunits offer an efficient solution Floating laws cope well with reconfiguration activities Equational reasoning is inadequate for reconfiguration Lack of tool support -calculus is instead supported by verification tools TyPiCal HAL, etc… Wepi has to be intended as a a front end for modelling with the the pi-calculus as the verication bytecode Web π vs π-calculus π
- 33. Conclusions (1) The standard notion of correctness used in process algebras is congruence based on bisimulation. Congruence is not always applicable for verifying the correctness of models For example, the requirements of the case study are not all expressible as congruencies between processes
- 34. Conclusions (2) It is easier to model workflow reconfiguration in Webpi than in the asynchronous pi-calculus Modelling would be even easier in a synchronous version of Webpi Model checking is more widely applicable than equational reasoning based on congruencies for verifying workflow reconfiguration
- 35. Analysis of requirements Synopsis of formalisms Development of ad-hoc formalisms Application to modeling and verification of case studies Implementation of workflow reconfiguration in WS-BPEL Major Contributions
- 36. Questions? "Did science promise happiness? I do not believe it. It promised truth, and the question is to know if we will ever make happiness with truth." (Emile Zola)