Wspólnotowy Serwis Informacyjny Badan i Rozwoju - CORDIS

Case study: a service component-based depannage service

The FTR&D application is a telecommunication service built on top of an embedded platform and using a large number of service components. The complete application developed for OMEGA is a service called Depannage. This service allows a user (the subscriber) to make a phone call and ask for help from a doctor, the fire brigade, a car maintenance service, etc. The Depannage service should locate an available service provider according to the request and as close as possible to the location of the (mobile) caller and connect the caller to the provider.

FTR&D used during the project a set of techniques in order to build the application by a step-by-step approach. First, we describe a high level specification of the service and component behaviour, including the behaviour of the communication between these components. This description includes timed constraints. Then the consistency of this high level specification is validated with respect to end-to-end requirements. This analysis is made with live sequence charts (LSCs), the Play-Engine tool and simulation/animation. In a second step, model-checking techniques are used with the Play-Engine tool in order to formally verify some requirements. The Play-Engine tool using the smart play-out extension allows executing and verifying scenario-based models with timed constraints. The complexity of verification and the current restrictions on the LSC subset supported by smart play-out implied identifying parts of the model focusing on complex and/or critical behaviours and applying verification to these parts rather than to the entire model. Once these first steps done, a more complete model (with all the potential behaviours, including creation and destruction of objects) is elaborated using the Rose CASE tool. This model is then exported to the IF/IFx tool and it is validated with respect to some requirements expressed by observers.

Evaluation summary
Application of LSCs and animation with Play-Out: The wish to specify components in a reusable way requires that the component specification should be done independently of any embedding architecture. Such specification corresponds to a universal LSC describing how the component will react to events coming from its provided ports and how (and when) this component will act on its required ports. For the system, the complete application, the specification should be enhanced by universal LSCs describing the communications between these components. Such LSCs could include time constraints and delays on the communication. The end-to-end requirements are expressed by existential LSCs and will be validated during the simulation/animation of the model. Our experience in OMEGA showed that LSCs and the Play-Engine tool allow a convenient way for specifying and executing high level requirements that seems well suited to the telecommunication domain.

Application of smart play-out to timed verification: The model checking tools allows formal verification of the expressed requirements. In order to use the model checking tools, currently some restrictions need to be made on the model: no symbolic instances, only one parameter for each signal. We have also to restrict verification on parts of the model in order to avoid state-explosion. It means that we have to focus our work on the more critical part of the behaviour. We can then verify that all possible executions of the model satisfy the specified requirements. The Smart Play-Out approach allows executing all the execution paths while searching for the satisfaction of a property (an existential LSC). This approach has been applied successfully to the Depannage model. Research to extend the LSC subset supported by smart play-out and to improve scalability is a central direction that will be pursued beyond the OMEGA project.
Application of the IF/IFx tool for formal specification and verification of complete systems. The objectives of our work with the IF/IFx tool were to make a formal verification of a more complete model. The model developed here includes more complex behaviours corresponding to the call termination. It involves the creation and destruction of objects and more complex message exchange patterns. In this model, we introduce also another behaviour that has not been completely described with the LSC tool. We were very satisfied by the use of the OMEGA/IF approach for the modelling and verification of our application. The main characteristics of telecommunication models and their properties could easily be modelled: non- determinism, different kinds of message exchanges, time constraints and timers, etc. The verification techniques are complete and efficient: simulation, exhaustive simulation and observer verification.

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