A specific system or situation being modeled is called a *scenario*. The model of a scenario in a domain theory consists of model fragments instances from the theory that are activated by the scenario definition.

The role of a modeling engine, such as DME, is to identify the set of model fragment instances that are active in a scenario and compose a mathematical model from the consequences of the activated instances. This mathematical model may then be simulated or analyzed.

The semantics of CML is defined in logic. This allows the use of
logic-based tools such as *Ontolingua* to provide analysis of
the domain theory itself. CML contains a hierarchy of foundation domain theories, including sets, dimensions, and units of measure. These foundation theories were developed as ontologies in the ARPA Knowledge Sharing Effort.