Web services are gaining popularity for supporting reusable business processes across distributed and heterogeneous environments. Current Web services are understood as taking inputs, executing their internal logic, and delivering outputs. When outputs are delivered, the interaction related to the given service ends. However, in many cases, the delivery of a service does not mean that the business transaction has ended, because there may be a change or cancellation of the original request (from the service requester) or an update of results (from the service provider). Current approaches deal with such scenarios by creating additional operations, thereby arbitrarily splitting the business logic and thus complicating service modeling and execution. This paper introduces the persistence of services via commitments. Commitments represent agreements between service requesters and providers. The commitments must be fulfilled to ensure successful business transactions. A commitment may last longer than individual episodes of service request and delivery. Operations on commitments, such as create, update, cancel, and discharge, reflect the persistence of the corresponding services and assist in constructing service models and protocols. We show that commitment-enhanced Web service descriptions are simpler and yet more general than current approaches, so that reliable and flexible service compositions can be produced.
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