To provide a service contract where the requirements of a service provider and a user are described by preparing a service contact to designate a clear rule concerning the dialogs necessary for a party during a transaction needed for the service.

The execution code components 502 and 512 are generated from a single service contact 514 and executed by a service execution engine 510 and a client engine 516 respectively. The contract 514 shows the specifications of clear rules concerning the dialogs necessary for the use of business services, and these specifications are exclusively produced and owned by a service provider. Then the contact 514 designates all dialog patterns that are permitted by a client and expresses the necessary dialog pattern operations of the service provider. Thus, a clear rule concerning the dialogs necessary for a party is designated during a transaction needed for the service.