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A Proof Based Approach for Modelling and VerifyingWeb Services Compositions

The Web Services composition defines a processthat involves various independent Web Services to performa complex function. This process is described with a standardlanguage (BPEL) and executed by tools supporting thislanguage. This kind of languages describes the behavior ofdifferent distributed services together, but it does not supportthe verification nor the validation of behavioral requirements.In our work, we are interested in the formal validation ofWeb Services composition. Formal models are extracted fromBPEL specifications and checked. Most previous work is basedon Web Services composition formalizations using Petri nets,process algebra or transition systems. The model checkingtechnique is set-up to validate such descriptions.In this paper, we present a proof and refinement basedapproach for the formal representation, verification and validation of Web Services compositions using the Event B method.

Stepwise Design of BPEL Web Services Compositions: An Event_B Refinement Based Approach

Several web services compositions languages and standards are used to describe different applications available over the web. These languages are essentially syntactic ones, their descriptions remain informal and are based on graphical notations. They do not offer any guarantee that the described services achieve the goals they have been designed for. The objective of this paper is twofold. First, it focusses on the formal description, modelling and validation of web services compositions using the Event_B method. Second, it suggest a refinement based method that encodes the BPEL models decompositions. Finally, we show that relevant properties formalized as Event_B properties can be proved. A tool encoding this approach is also available.

Animating Event B Models by Formal Data Models

We present a formal approach allowing to animate event B formal models. Invariants, deadlock freeness properties are expressed and proved on these models. This paper presents an approach that suggests to complete the proof activity in the event B method by animation activity. The obtained animator may be used to check if the event B models obtained fulfill user requirements, or to provide a help to the developer when describing its formal event B models and particularly in defining event B invariants and guards. More precisely, event B models are translated into data models expressed in the EXPRESS formal data modeling technique. The obtained data models are instantiated and provide an animation of the original B models. Following this approach, it becomes possible to trigger event B models, which themselves trigger entity instantiation on the EXPRESS side. As a further step, we show that the B models can be used as a monitoring system raising alarms in case of incorrect systems behavior. The proposed approach is operationally implemented in the B2EXPRESS tool which handles animation of event B models. It has been experimented for the validation of multimodal human interfaces in the context of VERBATIM project.

Validation et vérification formelles de systèmes interactifs multi-modaux fondées sur la preuve

This paper focuses on the formal validation and verification of multi-modal human computer interfaces. It describes part of the obtained results of the French RNRT VERBATIM project. It focuses on the application of a formal proof based technique, namely the event B method. We outline the capability of this technique to support the design of multi-modal human computer interfaces, in particular, the capability to support the expression and the verification of properties issued from the CARE family. The proposed approach uses notations and semi-formal techniques issued from the HCI design area.

Formal Modelling of Domain Constraints in Event-B

When designing a hardware or a software system, the integration of domain constraints becomes a determining factor to ensure a great match with the system requirements. This domain knowledge is most often modelled using ontologies that allow to express the domain data properties. In this paper, we propose an approach to integrate domain ontologies into a system development process based on Event-B. It consists to annotate Event-B models using the ontology concepts, this assumes a formalization of the domain ontology in the Event-B method. Therefore, we propose an extensible generic transformation approach which develops an Event-B specification based on an ontology described in an ontological language. The integration of the Event-B description of a domain ontology allows to constrain the system under design with the domain ontology and to validate domain properties.

Modelling information fission in output multi-modal interactive systems using event-b

Output multi-modal human-machine interfaces combine semantically output medias and modalities to increase interaction machine capabilities. In order to provide a rigorous development approach for these interfaces, we have proposed a generic formal model that formally describes the output multimodal interface construction starting from the information generated by the functional core. This formal model is composed of two sub-models: the first one dedicated to the semantic fission of information and the second one relative to the allocation of modalities and medias for information. This paper presents an Event-B implementation of the semantic fission submodel.

Développements formels d'interfaces multimodales fondés sur la preuve et le raffinement. Scénarios de développement

The software architecture models of interactive systems are based on the separation of the functional core from the interface itself. The development of this two modules implies the use of several different software engineering techniques and approaches. Due to the resulting heterogeneity, the validation of the system may become a hard task.ln the context of the RNRT Verbatim project, the study of different development scenarios for multimodal human interfaces has been conducted within the formal event B method. Refinement of specifications is put into practice in order tu structure developments and proofs for establishing the relevant properties of the system. The main interest of this paper is the link between both functional core and interface modules. Four different development scenarios are studied and compared.

Verification and Validation of Web Service Composition Using Event B Method

The Service-Oriented Architecture based on the Web service technology emerged as a consequence of the evolution of distributed computing. One of the key ideas of this technology is the ability to create service compositions by combining and interacting with pre-exisiting services. A service is implemented, described[1], and published by a service provider in a UDDI[2] registry. The service composition is referred to an executable process that interacts with other services accomplishing its functional goal. Orchestrationand Choreography[3] are the processes that allow to schedule the defined services compositions and messages exchanges. There is a wide range of industrial standardization efforts towards providing specification languages for the Web service composition. Among them BPEL (Business Process Execution Language[4]) is the most known and used orchestration language. Our work addresses the composition expressed by the orchestration and its support language BPEL. BPEL allows the designer to represent service compositions by various behavioral properties like services interactions (message exchanges), control flow constraints (sequence, iteration, conditional) or data flow constraints (exchange, modification, evaluation of data expressions).