Patrice Moreaux

An Integrated Framework for Web Services Orchestration

Currently, Web services give place to active research and this is due both to industrial and theoretical factors. On one hand, Web services are essential as the design model of applications dedicated to the electronic business. On the other hand, this model aims to become one of the major formalisms for the design of distributed and cooperative applications in an open environment (the Internet). In this article, the authors will focus on two features of Web services. The first one concerns the interaction problem: given the interaction protocol of a Web service described in BPEL, how to generate the appropriate client? Their approach is based on a formal semantics for BPEL via process algebra and yields an algorithm which decides whether such a client exists and synthesizes the description of this client as a (timed) automaton. The second one concerns the design process of a service. They propose a method which proceeds by two successive refinements: first the service is described via UML, then refined in a BPEL model and finally enlarged with JAVA code using JCSWL, a new language that we introduce here. Their solutions are integrated in a service development framework that will be presented in a synthetic way.

Sub-stochastic matrix analysis for bounds computation-Theoretical results

Performance evaluation of complex systems is a critical issue and bounds computation provides confidence about service quality, reliability, etc. of such systems. The stochastic ordering theory has generated a lot of works on bounds computation. Maximal lower and minimal upper bounds of a Markov chain by a st-monotone one exist and can be efficiently computed. In the present work, we extend simultaneously this last result in two directions. On the one hand, we handle the case of a maximal monotone lower bound of a family of Markov chains where the coefficients are given by numerical intervals. On the other hand, these chains are sub-chains associated to sub-stochastic matrices. We prove the existence of this maximal bound and we provide polynomial time algorithms to compute it both for discrete and continuous Markov chains. Moreover, it appears that the bounding sub-chain of a family of strictly sub-stochastic ones is not necessarily strictly sub-stochastic. We establish a characterization of the families of sub-chains for which these bounds are strictly sub-stochastic. Finally, we show how to apply these results to a classical model of repairable system. A forthcoming paper will present detailed numerical results and comparison with other methods.

A Formal Semantics and a Client Synthesis for a BPEL Service

A complex Web service described with languages like BPEL4WS, consists of an executable process and its observable behaviour (called an abstract process) based on the messages exchanged with the client. The abstract process behaviour is non deterministic due to the internal choices during the service execution. Furthermore the specification often includes timing constraints which must be taken into account by the client. Thus given a service specification, we identify the synthesis of a client as a key issue for the development of Web services. To this end, we propose an approach based on (dense) timed automata to first describe the observable service behaviour and then to build correct interacting clients when possible. The present work extends a previous discrete time approach and overcomes its limitations.

Structured performance analysis for component-based systems

The component-based system (CBS) paradigm is now largely used to design software systems. In addition, performance and behavioural analysis remains a required step for the design and the construction of efficient systems. This is especially the case of CBS, which involve interconnected components running concurrent processes. This paper proposes a compositional method for modelling and structured performance analysis of CBS. Modelling is based on stochastic well-formed nets (SWNs), a high level model of stochastic Petri nets, widely used for dependability analysis of concurrent systems. Starting from the definition of the system given in a suitable architecture description language, and from the definition of the elementary components, we build an SWN of the global system together with a set of SWNs modelling the components of the CBS and their connections. From these models, we derive performances of the system thanks to a structured analysis induced by the structure of the CBS. We describe the application of our method through an example designed in the framework of the CORBA component model.

Performance evaluation of Fractal component-based systems

Component-based system development is now a well accepted design approach in software engineering. Numerous component models have been proposed, and for most of them, specific software tools allow building component-based systems (CBS). Although these tools perform several checks on the built system, few of them provide formal verification of behavioural properties nor performance evaluation of the resulting system. In this context, we have developed a general method associating to a CBS, a formal model, based on stochastic well formed nets, a class of high-level Petri nets, allowing qualitative behavioural analysis together with performance evaluation of this CBS. The definition of the model heavily depends on the (run time) component model used to describe the CBS. In this paper, we instantiate our method to Fractal CBS and its reference Java implementation Julia. The method starts from the Fractal architectural description of a system and defines rules to systematically generate element models of the CBS and their interactions. We then apply a structured method for both qualitative and performance analysis, taking into account the given implementation of the Fractal model. The main interest of our method is to take advantage of the compositional definition of such systems to carry out an efficient analysis. The paper concentrates on performance evaluation and presents our method step by step with an illustrative example.

Performance evaluation of distributed database—A banking system case study

Abstract This paper presents a case study of performance evaluation of a distributed database system: a real banking system with several branches interconnected via a Wide Area Network. Due to the complexity of such systems, we use Stochastic Well Formed Petri nets to model its activities; the model obtained allows computation of its performance indices. This is done by taking into account the dimensional parameters, the behaviour of the clients submitting requests and the number of clients, the WAN contention and the locality level of the database. Synthesizing these various results, we propose configuration settings matching given workloads and system structures.

Reconfiguration of a Distributed Information Fusion System

Information Fusion Systems are now widely used in different fusion contexts, like scientific processing, sensor networks, video and image processing. One of the current trends in this area is to cope with distributed systems. In this context, we have defined and implemented a Dynamic Distributed Information Fusion System runtime model. It allows us to cope with dynamic execution supports while trying to maintain the functionalities of a given Dynamic Distributed Information Fusion System. The paper presents our system, the reconfiguration problems we are faced with and our solutions.