Top-level Forms

 

The primary top-level defining forms being supported are:

• defRelation for defining logical relations.
• defQuantityFunction for defining quantities used in the domain theory.
• defModelFragment for describing the behavior of modelled entities under explicitly specified conditions. Model fragments are used to describe phenomena that arise out of the interactions of a composite set of objects (e.g., collisions or flows), or the behavior of a single object (e.g., a resistor, pump, or valve).
• defEntity for defining properties of objects (e.g., resistors, containers) with time-dependent properties.
• defScenario for defining initial value problems consisting of a set of objects, their configuration, and initial values for the quantities that describe them.

In addition, the forms defDimension, defUnit, and defConstantQuantity are provided for defining new or derived dimensions, new or derived units, and universal constants, respectively.

A domain theory is a finite set of top-level forms. This implies that the order of forms in a domain theory is irrelevant and that implementations must allow for use before definition. This property of the language follows from its logical semantics. It is also a practical necessity because of the way in which time is handled. Because time must be made explicit, it is necessary to know whether a particular relation or function is time-dependent. This information is only available in the appropriate defining form.

The general syntax of a form is the form identifier (e.g., defQuantityFunction), followed by its name, followed by a series of keyword / value pairs. Some keywords are optional, as indicated by the surrounding brackets in the grammar (i.e., []). If an optional field is absent, its value defaults to NIL.

Wherever a keyword/value pair appears, an arbitrary number of other, implementation specific, keywords are allowed. If the domain theories employing such keywords are to be portable, however, the following restriction must be satisfied. If the keywords affect the behavioral inferences entailed by the domain theory, then they should only strengthen or annotate the behavioral inferences. This allows other implementations to ignore the additional keywords and still draw correct, if weaker conclusions. Domain theories that employ an extension that satisfies this criterion will be sharable across implementations.

The semantics of each top level form is defined by an axiom schema.

• defRelation
• defQuantityFunction
• Forms for defining model fragments
  • Syntactic Sugar
  • Semantics
  • defScenario
• defDimension, defUnit, defConstantQuantity