Extending OWL for QoS-based Web Service Description and Discovery

1 Main Theme of Thesis Web Services (WSs) are modular, self-describing, loosely-coupled, platform and programming language-agnostic software applications that can be advertised , located and used across the Internet. They are viewed as one of the promising technologies that could help business entities to automate their operations on the web on a large scale by automatic discovery and consumption of services. Based on the above reasons, the WS paradigm is being adopted by many companies and individuals and many WSs are being deployed and running. However, as all of these WSs are advertised in a UDDI-based repository, an unavoidable fact as UDDI is a de-facto standard, the problem of discovering them based on a requester's functional needs becomes crucial. UDDI uses a syntax-based approach for WS description leading to purely syntactic discovery efforts returning imprecise and inaccurate results. OWLS [OWL-S Coalition 2003] and similar joint Semantic Web and WS efforts solve the problem of syntactic WS description by using ontologies for describing WSs. Ontologies provide meaning to concepts and relationships between them, leading to semantic WS Discovery algorithms, which provide more precise and accurate results. But even if all the advertised WSs satisfying a requester's functional needs are returned, many results may be produced. So a non-functional concept is needed that will differentiate between the functionally equivalent WS advertisements. This concept is quality of service (QoS). QoS is closely related with the performance of a WS as well as with other features of a WS that bear on its ability to satisfy stated or implied needs. Therefore it has a substantial impact on users' expectations from a service. Thus WS descriptions must be enhanced with QoS descriptions. Additionally, WS discovery algorithms should perform QoS-based matchmaking and selection in order to produce fewer ranked results. Unfortunately, all the current research efforts fail in correctly describing QoS for WSs. Semantics seems to be missing from the QoS description of a WS leading to purely syntactic QoS-based WS matchmaking and selection algorithms. But even if semantics is introduced, QoS description is not rich enough and not quite extensible. So the main issue of this PhD thesis is the rich, extensible, and semantic description of QoS for WSs. Additionally, new QoS-based WS matchmaking and selection algorithms must be devised or the current best should be extended in order to take advantage of this enhanced semantic QoS description.