Enabling end-to-end support for non-functional properties in web services

Abstract

Current web services specification languages like WSDL and OWL-S are only focused on functional description. An important component that is missing from these specifications is the non-functional description such as its quality of service (QoS), cost, availability, etc. A comprehensive service description which provides information on non-functional aspects also is essential for tasks such as service selection, dynamic adaptation, etc. However, as many non-functional properties (NFPs) tend to be dynamic, mechanisms are needed to regularly update the NFP description with actual values obtained by proper monitoring. While there has been some efforts on specification of NFPs they are not general enough for representing at the desired granularity (operation, interface, etc.) and don't specify how these values should be measured and updated. Also, efforts on monitoring of NFPs are not closely related to description and dissemination of updated values. Hence, current approaches for handling NFPs are piecemeal and insufficient. In this paper, we present an integrated approach for enabling end-to-end support for NFPs from description, to measurement and updation, to dissemination of updated values. We describe a uniform representation for NFPs and propose mechanisms for specifying these NFPs for various service elements. The proposed NFP specification is generic enough to be used with any service description standard (such as WSDL, OWL-S, etc.) or as a separate specification paired with these standards. However, in this paper we use WSDL to illustrate specification of NFPs for various service elements. We then present a generic architecture for automatically measuring and updating the values of NFPs in a middleware. Further, we demonstrate its use by providing an implementation in Apache AXIS middleware for measuring and updating the values of dynamic properties automatically and making it available to clients.