Constraints for Service Contracts

This paper focuses on client-service interactions distinguishing between three phases: negotiate, commit and execute. The participants negotiate their behaviours, and if an agreement is reached they commit and start an execution which is guaranteed to respect the interaction scheme agreed upon. These ideas are materialised through a calculus of contracts enriched with semiringbased constraints, which allow clients to choose services and to interact with them in a safe way. A concrete representation of these constraints with logic programs is straightforward, thus reducing constraint solution (and consequently the establishment of a contract) to the execution of a logic program.