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WSMX Execution Semantics

WSMX Execution Semantics. Executable Software Specification Eyal Oren DERI eyal.oren@deri.org. Background information. WSMX: execution environment for dynamic discovery, selection, mediation and invocation of semantic web services

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WSMX Execution Semantics

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  1. WSMX Execution Semantics Executable Software Specification Eyal Oren DERI eyal.oren@deri.org

  2. Background information • WSMX: execution environment for dynamic discovery, selection, mediation and invocation of semantic web services • WSMX is built on WSMO: services, ontologies, goals and mediators • WSMX: manages repository, achieves user’s goal by selecting matching service, mediating and invoking WSMX execution semantics

  3. Designing WSMX • Conceptual model: what are we talking about • Architecture: components, how they interact • Execution semantics: system behaviour WSMX execution semantics

  4. What did we do? • Design of WSMX includes formalspecification of system behaviour • Reasons: • enlarging developers’ understanding of the system • proving properties of the system • enabling model-driven component execution • We present the execution semantics of WSMX • Did our approach address the objectives? WSMX execution semantics

  5. What are execution semantics? • Four phases in software development: requirements, design, implementation, testing • Formal methods can be used during design: to improve the design process and the result • Formal method: a mathematically-based language for specifying systems • Execution semantics: aformal definition of operational behaviour of a system. WSMX execution semantics

  6. Why model execution semantics? • Formal methods do not make correct programs! • Increase understanding and agreement between project members (by explicit specification process) • To checkproperties of the constructed specification: discover future properties of the modelled system WSMX execution semantics

  7. Why model execution semantics? • Execute thespecification • general idea: specification is input for executionengine; engine executes model, informs components to perform a task (workflow management, business process management) • main argument in favour: flexibility, not hard-coding this interplay, no need to translate specification into programming code • main argument against: inefficient implementation; might not be important: if composition is simple and components themselves are implemented efficiently WSMX execution semantics

  8. Requirements • Enlarge developers’ understanding: technique must be easily readable yet unambiguous • Check properties of the system: technique must be formal and have a proof system • Automate coordination between components: technique must have operationalisation, and execution procedure for a model WSMX execution semantics

  9. How to model execution semantics? • We want to automate control flow between components • Components treated as black-boxes: we know their functionality but not how they operate • Using Petri nets • graphical, supposedly easily understood • formalised, well analysable • executable WSMX execution semantics

  10. WSMX execution semantics (see paper) WSMX execution semantics

  11. Using execution semantics • The goal was: • understandability • model checking • model-driven execution • Did this work? WSMX execution semantics

  12. Did it work? • Understandability • not easily readable: syntax is very simple, but model gets complex • hard to write and time-consuming to maintain • simulation is very helpful • Executingspecification • technical problems: synchronous invocation from the engine • work in progress – the general idea is ok WSMX execution semantics

  13. Did it work? • Model checking • large amount of work on problems in Petri nets (algorithms, tools, decidability & complexity results) • however, we did not use this possibility: • during implementation developers had to manually translate the Petri net specification into Java code. • but model is not easily readable: implementation did not strictly follow model! • model checking not very useful WSMX execution semantics

  14. Conclusion • Specifying execution semantics as part of software development • Three objectives: understandability, model checking, component execution • Used Petri nets to specify the behaviour of WSMX • Petri nets are not a useful technique for this specification: • not easily readable (and not easily writable) • model checking and executability in principle possible WSMX execution semantics

  15. Future • Investigate other techniques that overcome these problems • take into account: we want to do model checking and execute the specification • UML Activity diagrams: easily readable, more intuitive, no model execution • YAWL: builds on Petri nets, designed for usability, no good tools yet • Separate techniques: • use one model for proving and executing • use second model for clarification and understanding • (second would be generated from the first) WSMX execution semantics

  16. Questions? WSMX execution semantics

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