Automatic quality of service adaptation for composite web services

Quality of Services (QoS) management has become an important issue for Web services. Indeed, QoS is becoming a crucial and a distinguishing criterion among functionally equivalent Web services. QoS Management consists of two complementary tasks: monitoring and adaptation. Both are very challenging because of the unpredictable and dynamic nature of Web service composition. We are motivated to solve the QoS problem by taking advantage of some characteristics of composite Web services, such as their similarity to traditional workflows. In this thesis, we propose a broker based architecture that enables dynamic QoS monitoring and adaptation for composite Web services. Our approach consists of dynamically changing the execution paths of composed Web services by instrumenting the BPEL process. A new construct flexPath is introduced for supporting alternate execution paths definition in BPEL. We developed a BPEL compiler allowing automatic instrumentation for BPEL definition files. The BPEL process is deployed using the instrumented definition files in order to interact with the QoS broker during execution. The QoS broker is a key component in our architecture and is responsible of monitoring the QoS and managing the adaptation. We propose a broker that enables runtime monitoring of QoS, prediction of potential QoS violation, and the selection of the best execution path of the process in order to improve QoS when needed. We developed a prototype to evaluate our proposed architecture. A case study is also presented through an example BPEL process and a number of partner Web services. The performance of the QoS adaptation has been analyzed and the results showed that the QoS of the BPEL process has been considerably adapted and improved comparing to the original one. In addition, we analyzed the major factors that affect the performance of our prototype tool

A Survey on Service Composition Middleware in Pervasive Environments

The development of pervasive computing has put the light on a challenging problem: how to dynamically compose services in heterogeneous and highly changing environments? We propose a survey that defines the service composition as a sequence of four steps: the translation, the generation, the evaluation, and finally the execution. With this powerful and simple model we describe the major service composition middleware. Then, a classification of these service composition middleware according to pervasive requirements - interoperability, discoverability, adaptability, context awareness, QoS management, security, spontaneous management, and autonomous management - is given. The classification highlights what has been done and what remains to do to develop the service composition in pervasive environments

Dynamic integration of context model constraints in web service processes

Autonomic Web service composition has been a challenging topic for some years. The context in which composition takes places determines essential aspects. A context model can provide meaningful composition information for services process composition. An ontology-based approach for context information integration is the basis of a constraint approach to dynamically integrate context validation into service processes. The dynamic integration of context constraints into an orchestrated service process is a necessary direction to achieve autonomic service composition

QoS-Aware Middleware for Web Services Composition

The paradigmatic shift from a Web of manual interactions to a Web of programmatic interactions driven by Web services is creating unprecedented opportunities for the formation of online Business-to-Business (B2B) collaborations. In particular, the creation of value-added services by composition of existing ones is gaining a significant momentum. Since many available Web services provide overlapping or identical functionality, albeit with different Quality of Service (QoS), a choice needs to be made to determine which services are to participate in a given composite service. This paper presents a middleware platform which addresses the issue of selecting Web services for the purpose of their composition in a way that maximizes user satisfaction expressed as utility functions over QoS attributes, while satisfying the constraints set by the user and by the structure of the composite service. Two selection approaches are described and compared: one based on local (task-level) selection of services and the other based on global allocation of tasks to services using integer programming