Modeling knowledge is captured in a general purpose domain theory that describes a class of related phenomena and systems. A domain theory consists of a set of quantified definitions, called model fragments , each of which describes some partial piece of the domain's physics, such as processes (e.g., liquid flows), devices (e.g., transistors), and objects (e.g., containers). Each definition applies whenever there exists a set of participants for whom the stated conditions are satisfied. A specific system or situation being modeled is called a scenario. A model of the scenario consists of fragments that logically follow from the domain theory and the scenario definition.
A typical implementation supporting CML might be used as follows to predict the behavior of a chemical processing plant. A domain theory is constructed that describes the objects, systems, and phenomena present in a typical chemical processing plant. The theory would include physical phenomena such as mass and heat flows, boiling, evaporation, and condensation; it would also include chemical reactions, the effects of catalysts, and models of components such as reaction vessels, pumps, controllers, and filters. Constructing such a domain theory is a substantial undertaking. A major goal of CML is to support the interchange and reuse of such theories.
Once the domain theory has been constructed, it can be used to model many different processing plants under a variety of different conditions. The user specifies a scenario that defines an initial configuration of the plant, the initial values of some of the parameters that are relevant to modeling it, and perhaps conditions that further characterize the system. The CML implementation automatically identifies model fragments that are applicable in the scenario. These model fragments are composed into a single model that comprises both a symbolic description as well as a set of governing equations. The equations may be solved or simulated to produce a behavioral description. Because the conditions under which the model fragments hold are explicit in the domain theory, the system automatically constructs additional models that describe the plant as it moves into new operating regions.