Methods for Improving QoS-driven Management of Web Services and their Service Level Agreements

The Internet is today subject to growing needs of information exchanges and modular applications. The Web now proposes information through different media (texts, pictures, videos, sounds) available on different websites (social networks, blogs, hosting sites) reached from a large set of devices (PCs, PDAs, smartphones). The data transfered is related to an infinite amount of topics as stock exchange information, picture editing or flight booking. To cope with such possibilities, one of the most fitted solution is offered by the use of Web Services. Web Services are self-describing, open components that support rapid, low-cost composition of distributed applications over the Web. Web Services Management tackles issues as installation, configuration, collecting metric and tuning to ensure responsive service execution. Improving the management of Web Services is essential to increase the adoption of Web Services and to impose the adoption of standards. There are different possibilities to improve Web Services management but managing services through quality offers large opportunities. The emergence of Web Services involves an increasing number of available services on the Internet. A service requester is then faced to a large choice while it executes a service. Indeed, a particular functionality can be offered by numerous Web Services emanating from multiple providers. To discriminate among available services, the requester has to compare the quality levels offered by providers. Quality provides several opportunities to respond to most management issues (i.e.: service monitoring, performance measurement, capacity planning) and, more specifically, allows to differentiate functionally equivalent services. This thesis presents a set of contributions related to the management of Web Services through quality information. The first significant contribution we made is a quality model that enables stakeholders of the service execution to specify their capabilities and expectations about quality. This model is essential to allow a quality driven management of Web services. The quality model is used by stakeholders to express involved quality criteria, measurement functions, precisions about favored qualities and quality information that are necessary to manage Web services. The second important contribution proposed in this work is a set of methods improving the management of Web services with help of quality information specified by stakeholders of the service execution. Three different methods are proposed: (1) A selection method which defines the best service according to non-functional requirements of the requester while multiple services are available to perform the same task at different quality levels. (2) A composition method which defines the best available composition of services to perform a complex task involving several services. (3) The last method proposed is a model enabling to determine the profile of a requester based on quality evaluations given to past services execution. The profiling method allows to automatically recommend to the requester services that correspond to his quality expectations. The last essential contribution of this thesis concerns the management of Service Level Agreements that allows to define quality contract between services requesters and providers. We propose two models enabling to improve the SLA control and monitoring. (1) The first model relies on normative autonomous agents managing services activities. In our proposal, normative agents are able to control the execution of a service while observing its quality conformance. (2) The second proposed model enables to monitor a service execution through context information. Quality elements are related to different context categories and context modifications are handled in order to ensure the quality conformance to the initial contract.(DOCSESG00) -- FUNDP, 201