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Petri Nets and Software Engineering

Petri Nets and Software Engineering. Anis Yousefi a_yousefi@ce.sharif.edu. We attempt to…. illustrate different dimensions of software engineering (SE), to point out aspects of Petri nets that can be exploited to solve SE problems

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Petri Nets and Software Engineering

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  1. Petri Nets and Software Engineering Anis Yousefi a_yousefi@ce.sharif.edu

  2. We attempt to… • illustrate different dimensions of software engineering (SE), to point out aspects of Petri nets that can be exploited to solve SE problems • present a design methodology that extends UML using colored Petri nets

  3. Structure of our talk • Petri Nets and Software Engineering • Problem- vs. Solution- oriented disciplines • SE dimensions that can be supported by Petri nets • Why Petri nets? • limits of Petri nets in coping with SE problems • Verifiable Modeling Techniques Using a Colored Petri Net Graphical Language • UML and CPN • Orchestrate • Visio

  4. Petri Nets and Software Engineering

  5. Problem- vs. Solution- orienteddisciplines • problem-oriented disciplines : focus on problems and search for the best solutions regardless of the underlying methods or techniques • software engineering. • solution-oriented disciplines : focus on theory and offer it for different application domains • Petri net. • The meeting of problem- and solution-oriented disciplines can lead to important progresses in both areas!

  6. Useful applications of Petri nets • Requirement engineering • Reverse engineering • Design of user interfaces • Modeling and analysis of safety critical systems • Distributed systems • Real time systems • Multimedia systems • Software process management • Software performance evaluation

  7. SE dimensions that can be supported by Petri nets

  8. Why Petri nets? • The ability of easily modeling concurrency and synchronization aspects • The intuitive graphic notation • The formal semantics that supports powerful analysis capabilities

  9. Why Petri nets? (cont.) • The various extensions of Petri nets (in particular CPNs or, more generally, high-level Petri nets) are very useful for modeling many software engineering problems • Software engineering is dealing with new problems: pervasive computing, mobile applications, context awareness, … • The software engineering community is actively seeking new solutions and ideas to address these new problems. • Petri nets may provide useful support to some new challenges.

  10. limitsof Petri nets in coping with software engineering problems • mastering complexity and size : Software engineers need flexible, adaptable and scalable modeling notations. • Petri nets, as many other formal methods, rarely provide the flexibility, adaptability, modularity and scalability required in software development. • But, hierarchy and object oriented extensions to add flexibility, adaptability and scalability, i.e., the modeling power needed for software engineers.

  11. A Verifiable Modeling Technique Using ColoredPetri Net Graphical Language

  12. Petri Nets for Specification and Verification • Software Engineers tend to use different modeling languages through the many phases of software development. • UML (Unified Modeling Language) is based on sets of modeling languages with different characteristics that is integrated in a unifying framework.

  13. The Problem • The Unified Modeling Language(UML) cannot perform formal model verification. • Adding executable semantics to UML provides the formalisms required for automated verification. • We want to present a design methodology that extends UML by verifying software designs using a colored Petri net (CPN)

  14. UML • UML : A language for specifying, visualizing, constructing, and documenting the artifacts of software systems, business modeling, and other nonsoftware systems. • Major drawback : • Its semantics are imprecise and vague (no executable semantics) Formal verification extremely difficult and expensive.

  15. CPN • Petri net : A simple graphical model consisting of places, transitions, and arcs. • Well suited for : complex systems in which communication, synchronization, and resource sharing are important. • The graphical representations can be translated into mathematical models by which the graph’s semantics can be analyzed, using formal proofs. • CPNs allow the use of a variety of formal analytical techniques : • to prove properties (e.g., safety properties, deadlock) • to calculate performance measures (e.g., response times, waiting times).

  16. CPN and UML • Major disadvantage : • Lack of commercially acceptable tools for developing Petri net models • Petri nets implemented with a standard interface can be used to extend UML capabilities overcoming UML’s lack of formalisms. • A drawing package + Orchestrate verification server(to verify and correct UML-based designs)

  17. Orchestrate • Extends UML with formal modeling techniques based on CPNs • Allows systems to be designed informally in UML from inside the drawing package and then translated into a CPN for formal verification. • Implemented as a Web service and written in Java, the Orchestrate system provides a Web-server-based verification engine to client programs. • Any drawing package that is programmable and able to use Web services can work with Orchestrate as the graphical user interface (GUI).

  18. Orchestrate (cont.) • Orchestrate is a server that verifies CPN models presented to it by clients and then returns the results of the verifications to the clients. • The CPN models submitted to Orchestrate are XML documents, as are the returned verifications. • Orchestrate does not provide a GUI. Instead, off-the-shelf drawing packages are used to provide the graphical semantics. • Visio 2000 • Visio’s key feature is support of a macro language capability that is used to translate the graphical designs into XML for submission to the Orchestrate server. • Visual Basic

  19. Visio • Using Visio’s PetriNet.vss template and its built-in Visual Basic control program, system designers convert the visualization of the design into the executable semantics of a CPN, as described in eXtensible Markup Language/Simple Object Access Protocol (XML/SOAP) • The Visual Basic program in the drawing package transmits the XML description of the graphical design to the Orchestrate server, which validates it. • The Orchestrate server returns the results to the Visio program, which displays the verification status by modifying the colors of the objects of the diagram.

  20. Visio (cont.) • Objects colored blue are valid CPN constructs; those colored red are invalid. The designer must revise the red paths until verification is completed. • While the designer works on the CPN model, the Orchestrate system automatically verifies each change in design and gives the user immediate feedback on potential flaws. • The designer continues to refine the model until the Orchestrate system verifies that it follows correct Petri net constructs.

  21. CPN routing constructs used by Orchestrate

  22. Activity diagram of an example UML-based design system

  23. Conversion of UML-based Design to CPN • To verify the UML-based design system, we must first convert the design to a CPN. • By hand! • The drawing package provides: • The drawing tools for the graphical semantics • Connects to the verification server.

  24. Designer view in Visio of CPN-based design session

  25. Corrected colored Petri net design

  26. Conclusions • The meeting of problem- and solution-oriented disciplines can lead to important progresses in both areas. • Petri nets have been successfully applied many times to several software engineering problems. • Translating UML-based diagrams into CPNs is not difficult and permits formal verification of UML-based designs.

  27. Future Work • Extension for the Orchestrate system : • Automatically converting UML into formal models, such as Petri net diagrams. • Since Visio supports the diagramming of UML, it should be possible to translate UML-based designs into CPNs, thus extending UML to support formal verification techniques.

  28. References • [1] Giovanni Denaro and Mauro Pezz`e, “Petri Nets and Software Engineering”, In: J. Desel, W. Reisig, G. Rozenberd Eds., Advances in Petri Nets Lecture Notes on Concurrency and Petri Nets, LNCS 3098 Springer-Verlag 2004. • [2] Ben M. Faul, “Verifiable Modeling Techniques Using a Colored Petri Net Graphical Language”, Technology Review Journal, Spring/Summer 2004.

  29. “ Thanks for your attention! ” Questions?

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