Zohra Sbaï

On the verification of business processes by model checking techniques

The correctness of a workflow specification is critical for the automation of business processes. For this reason, errors in the specification should be detected and corrected as early as possible - at specification time. In this paper, we present a verification method for workflow specifications using model checking techniques. We propose an approach for verifying correctness properties of workflow processes using SPIN model checker. First, a formalized workflow specification is translated into a Promela description. Second, the desired property is translated to an LTL formula. Finally, the SPIN model checker is run to check if the correctness properties hold for the model, and, if not, to provide a counterexample.

On Service Composition in Cloud Computing: A Survey and an Ongoing Architecture

Cloud computing has become a widely used concept. It is characterized by its elasticity, its on demand services and the unlimited provided resources. However, because of the complexity of customers service requests, their provision became an increasingly difficult task. In fact, in order to meet these requirements, services should be combined to implement a composite one performing the requested task. It is in this sense that the use of SOA architecture, which provides service composition, seems a useful solution. This paper investigates existing works on services discovery and composition in SOA as well as Cloud architectures. We study and compare these works and present an architecture of services composition based on SOA architecture and Cloud computing.

Towards a System for Cloud Service Discovery and Composition Based on Ontology

Cloud computing has become a widely used concept. It is characterized by its elasticity, its on demand services and the unlimited resources provided to end users. However, the increase of services number offered by different providers causes sometimes ambiguity problems. So, ontology must be used to relate between different services in order to facilitate their access. Many languages expressing ontology have been proposed namely RDF, OWL, etc. To access them, queries should be expressed using SPARQL. However, generally, users are not familiar with this query language. Therefore, there is a need to an interface allowing them to express their requirements without any expertise in SPARQL language. Besides, given the increase of complex service requirements, it is sometimes necessary to compose services to meet final user requirements.

On Expressiveness of TCTL^{\varDelta }_{h} for Model Checking Distributed Systems

Systems analysis is becoming more and more important in different fields such as network applications, communication protocols and client server applications. This importance is seen from the fact that these systems are faced to specific errors like deadlocks and livelocks which may in the major cases cause disasters. In this context, model checking is a promising formal method which permits systems analysis at early stage, thus ensuring prevention from errors occurring. In this paper, we propose an extension of timed temporal logic TCTL with more powerful modalities called \(TCTL^{\varDelta }_{h}\). This logic permits to combine in the same property clocks quantifiers as well as features for transient states. We formally define the syntax and the semantics of the proposed quantitative logic and we show via examples its expressive power.

CTL Model Checking of Web Services Composition based on Open Workflow Nets Modeling

Web services composition (WSC) has an enormous potential for the organizations in the B2B area. In fact, different services collaborate through the exchange of messages to implement complex business processes. BPEL is one of the most used languages to develop such cooperation. However, it has been proved that its use is complex and can require some expertise in XML syntax. Even its graphical representation is not evident to handle. This is why the authors propose to model Web services using oWF-nets, a subclass of Petri nets, and then, to translate them to BPEL. Whilst, a WSC is with added value only if the involved services are compatible. So in this context, across the translation proposed the researchers develop a verification layer of the WSC compatibility. Hence, they propose a framework named D&A4WSC which allows to model the WSC by oWF-nets, to check their compatibility with the model checker NuSMV and to translate them if they are compatible in BPEL processes using the oWFN2BPEL compiler. D&A4WSC permits, furthermore, to formally analyze a BPEL process.

On Compatibility Analysis of Inter Organizational Business Processes

Distributed systems are promisingly used in context of cross organizational enterprises. To develop these systems, Web services form an essential and wide accepted technology because they provide a significant level of platform independency and autonomy. Services are generally designed to interact with other services to form larger applications. In order to interact correctly with each other, Web services have to be compatible. This include not only composability of the involved services but also the correct execution of the overall composite service. In this context, we suggest in this paper to study the compatibility of Web services in different aspects and to provide a formal approach to characterize and verify this property. This approach is straightforward since it combines Petri nets and model checking techniques.

Model Checking of Cost-Effective Elasticity Strategies in Cloud Computing

Cloud computing is a revolution in how computing power is delivered to business. It offers different measured services to clients who require them by writing a simple request. These requests are becoming more and more complex so that services need to be composed to meet them. Additionally, these Cloud composite business services (CCBSs) need to be elastic, i.e. their number should be replicated or reduced according to the number of their user demands. Ensuring these two operations is done according to a well-defined strategy. We are interested in this paper in cost-effective elasticity one. Applying this strategy on CCBSs gives birth to a system that needs to be checked to insure that SLA constraints, such as deadline specified by the user, are not violated. In this paper, we present a formal model using Timed Coloured Petri nets to model, check and compare between these strategies before implementing them in real Cloud.

Towards TCTL h Δ model checking of time Petri nets

At present, the most common method for verifying that a system met its specifications or to detect unexpected behavior and issues is to perform simulations on the model. This approach is limited by the fact that it is of course impossible to be exhaustive and fully test the system. This is why the need to resort to formal methods, and more particularly to model-checking, was felt. In this paper, we are interested by modeling the behavior of real time systems using time Petri nets. Our main objective is to present new model checking algorithms for our new logic called TCTLhΔ which is the combination of the two extensions of the TCTL logic TCTLh and TCTLΔ. These algorithms are based on the concept of on the fly verification and are implemented into the model checker Romeo.

Model Checking Web Services Choreography

By exploiting the open standards of Web and by assuring a weak coupling of components, Web service technology provides a flexible and universal approach to the inter-operability of heterogeneous systems. This service composition is one of the major challenges of the emerging paradigm of Service Oriented Computing (SOC). Existing works suggest resolving this problem by the orchestration of services. However, this approach is centralized around a composition engine and there is a static service composition which follows a predefined pattern. To overcome this, a composition approach based on decentralized cooperation between a collection of services has been proposed, known as a choreography. The formal verification of such a composition is a very interested subject in the research area. Our contribution in this area is to provide a formal framework ensuring the verification of a choreography described in WS-CDL. For this, we propose first to model this choreography by a composition of open workflow nets: a special class of Petri nets. Then, we detail how to check behavioral properties specified in temporal logic using the model checker NuSMV.