A Cost Model for Participating Roles Based on Choreography Semantics

Emergence of web services have generated new business models, opportunities and challenges. One of the major challenge faced in effecting utilization of these web services is composition of non functional features such as performance, security and geographical affinity of these services. Existing standards do not address the composition of such non functional features. A formal model based on trace semantics and incorporating QoS have been proposed to estimate minimal/maximal/average cost of a given choreography. This trace semantics can not differentiate between different participants providing same kind of services in a collaboration. The cost attribute of a choreography is dictated by participating role instances rather than role type. A formal semantics of choreography incorporating this aspect has been presented in the literature. In this paper, we present a model of choreography with cost based on semantics which differentiates between participant roles and their types. Our model views the cost attribute of a participating role as structured one having two components. The first component of the cost is due to internal operations performed by a role whereas second component of cost is due to interaction with other roles. We demonstrate our model with an example.