Two problems-two solutions: one system-ECLIPSE

The constraint logic programming system ECLⁱPS^e is discussed. Computation in ECLⁱPS^e alternates between two modes: constraint handling and host program execution. The host programming language is (an extended) Prolog, which handles search, and interaction with the programming environment. The control for host program execution mode is the usual Prolog control. The constraint handling mode has a quite different form of control, which generalises data-driven computation. During constraint handling all possible information is extracted from the constraints. When there is no more information to be extracted, the system returns to host program execution, which continues until another constraint is posted and constraint handling restarts. The authors show the advantage of combining Prolog programming with constraints handling for a shift planning application. They also indicate how to control the constraint handling itself, and the application of such control for optimising job-shop scheduling programs