Secure choreography of cooperating Web services

The successful progress of the Web services concept demands flexible ways for Web services to cooperate and to jointly fulfill a task that is requested by a client. In some applications, the execution of the task is not completely specified beforehand, but could rather be referred to as "best effort". One example is information searches. A flexible invocation of cooperating Web services might mean that their identities are not known beforehand. To achieve trust in the outcome of the task, it is essential that the identities of the cooperating Web services can be tracked in a secure way. It is also essential that the requesting client can decide to what degree the task has been executed. In this paper an approach to securely track identities of Web Services is introduced. The use of one-way messages creates a system where the state of a request is presented by the request itself.