The present invention leverages a unilaterally-based interaction contract that enables applications to have a persistent state and ensures an exactly-once execution despite failures between and by communicating entities, permitting disparate software applications to be robustly supported in an environment where little is known about the implementation of the interaction contract. In one instance of the present invention, a web services interaction contract provides a communicating application with duplicate commit request elimination, persistent state transitions, and/or unique persistent reply requests. The present invention permits this interaction contract to be supported by, for example, a persistent application, a workflow, a transaction queue, a database, and a file system to facilitate in providing idempotent executions for requests from a communicating application.