Composing Web Services in an Open World: QoS Issues

Summary form only given. Orchestrating Web services has become the method of choice for building new services on top of existing ones, e.g., for business processes. Languages and methods have been developed and are now getting widely used, BPEL being the typical instance. When exposing the profile of a Web service, QoS parameters are typically specified. Besides security aspects, QoS involves a variety of parameters related to performance as well as quality of the returned data. How QoS should be handled in this context is the subject of my talk. A number of novel and not so well identified issues occur that make this topic deviating from QoS for networks in a substantial way. Firstly, since Web services aim at hiding details for the external world, no information regarding the infrastructure or resources supporting a Web service are exposed. This prevents from using classical resource based performance models; so contracts are preferred instead. A second important feature is that, unlike in networks, the control in orchestrations may depend on the carried data. Consequently performance and data interfere. These and other features make the subject of QoS for composite Web services a novel area offering plenty of non standard issues that I shall discuss.