Qos - based web service description and discovery
Κυριάκος Κρητικός · 2008
The success of the Web Service (WS) paradigm has led to a proliferation of available WSs.As these WSs are advertised in inter and intra-organizational registries/repositories, they have to be discovered based on the functional needs of the user.However, these registries rely on the current WS standard stack that uses WSDL and UDDI for WS description and discovery.Unfortunately, these two standard languages are based on the use of static descriptions of service interfaces and other general non-functional service attributes for publishing and nding WSs.This situation creates two problems.Firstly, syntactic discovery eorts return imprecise and inaccurate results.Secondly, no means are provided in order to select among multiple services that appear to perform the same function.The rst problem is solved by combining Semantic Web (SW) and WS technologies.Ontologies are used, which provide meaning to concepts and relationships between them and thus lead to semantic WS descriptions and discovery algorithms.These enhanced discovery algorithms equipped with SW technologies provide more precise and accurate results.One recent result of the joint SW and WS eorts is OWL-S, which is currently a W3C member submission.The second problem can be solved by taking into account a big subset of all possible non-functional properties of WSs, which is called QoS (Quality of Service).QoS is closely related with the performance of a WS as well as with other features and characteristics of a WS that bear on its ability to satisfy stated or implied needs.Therefore it has a substantial impact on user's expectations from a service and can be used as a discriminating factor between functionally equivalent WS advertisements.Thus WS descriptions must be enhanced with QoS descriptions.Additionally, WS discovery algorithms should perform QoS-based ltering (matchmaking) and ranking (selection) on WS advertisements in order to produce fewer ranked results.A QoS oer (or demand) of a WS is a set of constraints/restrictions on some QoS attributes that restrict them to have certain values (for unary constraints) or certain combinations of values (for n-ary constraints).Actually, the current modeling eorts of QoS oers or demands only dier in the expressiveness of these constraints.However, when it comes to QoS attributes/metrics modeling, these eorts fail.The rst reason is because the QoS attribute de nition is syntactic.Another reason is that the QoS attribute model is not rich enough, not incorporating the de nition of measurement units, currency units, measured properties and measurement methods.The last reason of failure is that the QoS attribute iii Pursuing a PhD is a truly life-changing journey that is not possible to accomplish without the help, support and guidance of many people.First of all, I would like to thank and express my gratitude to my advisor, Professor Dimitris Plexousakis, who gave me the opportunity to perform and accomplish the biggest step towards an academic or research career, which is the PhD acquisition.His continuous support encouraged and enabled me to surpass all research obstacles that came into my way.In addition, his expert guidance, stimulating encouragement, and valuable suggestions have greatly contributed to this thesis and helped me round o the PhD research successfully.Secondly, special thanks go to the other two members of my supervising committee, Professor Nikolaou and Associate Professor Koubarakis, for their cooperation, support and guidance in many parts of this work.Moreover, I would like to warmly