What constitutes a service on the web? - Towards a theory of services

• Klaus-Dieter Schewe
• Qing Wang

• Bernhard Thalheim
• Klaus-Dieter Schewe
• Andreas Prinz
• Bruno Buchberger

There are many approaches to modelling and development of service-orientedsystems, but there is still no convincing answer to what a (software)service is. In this chapter we discuss the various attempts to develop a theoryof services, identify aspects that have already been addressed, and extract gaps.This leads us to propose the BDCM² framework capturing behaviour, description,contracting, monitoring and mediation. For the behavioural model we refer to the two-layer model of Abstract State Services (AS²)capturing functional aspects ofdata-intensive web services. The model of
service mediators permits building complexapplications, in which parts are realised by services. Furthermore, we ighlight the decisive role of service ontologies for supporting the location of services as well as the capture of contractual aspects by means of service-level agreements (SLAs).Finally, we conclude that a contract is only as good as the means to monitor theagreements. While part of the research has already reached a promising level ofmaturity, some aspects are still in an infant state.