A Constraint-Based Approach for Developing Consistent Contracts in Composite Services

A key problem that challenges the designers of service-oriented systems is ensuring the consistency of composite Web service contracts based on their parameters. This paper utilizes constraint satisfaction approach to examine the problem at design time and by focusing on quality of service (QoS) contract parameters. It proposes a generic framework to formalize service contract composition as a constraint satisfaction problem (CSP). It also introduces an initial tool design for automating composite contract consistency checking and adaptation based on QoS parameters. The tool aims at supporting Web service orchestrators to specify appropriate contract parameter values and adapt them so that consistency of composite contracts is increased to some extent. Further, it enables them to analyze and reason about violation percentages during contract negotiation phase. The benefits of the proposed CSP framework and the tool design have been illustrated through a Stock Manager Web service composition scenario.