Generating Global Contract for Composite Services

Nowadays services are fast evolving into the coarse-grained composite services by mash up technology in both business and IT levels. It is quite important for both customers and composite service providers (called "broker") to measure whether the offered services would satisfy customers´ demands. However, recent researchers use only functional aspects and QoS features to describe customer´s demand and provider´s capability. QoS are not enough to accurately and comprehensively describe the agreement between the customer and the provider in terms of NFPs of the requested/offered service. Therefore, this paper proposes a formal model to describe the service agreement in terms of functional and non-functional aspects respectively using state transition and service contract. In addition, we discuss the contract conflict detection and contract composition rules, and then we provide an algorithm for generating composite service contract. Finally, the paper uses an entertainment ticketing service as an example to analyze and verifies the validity of the model mentioned above.