2.4 Requirements Specifications

How do we state the requirements that an abstraction must satisfy in order to belong to a concept? We focus here on one way (of many possible ways) of stating such requirements, using natural language. We first consider a simple concept description and then expand what concept descriptions can include in several useful ways.

A simple concept description has two parts, a syntactic part and a semantic part.

• The syntactic part describes the interfaces of the objects and operations; that is, in order to belong to the concept an abstraction must have certain objects and operations with certain external interfaces.
• The semantic part describes the properties that the objects and operations of an abstraction must have in order to belong to the concept.