USE is a system for the specification of information systems. It is based on a subset of the Unified Modeling Language (UML). A USE specification contains a textual description of a model using features found in UML class diagrams (classes, associations, etc.). Expressions written in the Object Constraint Language (OCL) are used to specify additional integrity constraints on the model. A model can be animated to validate the specification against non-formal requirements. System states (snapshots of a running system) can be created and manipulated during an animation. For each snapshot the OCL constraints are automatically checked. Information about a system state is given by graphical views. OCL expressions can be entered and evaluated to query detailed information about a system state. The picture below gives a general view of the USE approach.