Representing Knowledge in Two Distinct Descriptions: Extensional Vs. Intensional

摘要

A data description method for Computer Aided Design (CAD) is proposed. To describe entities and their abstract concepts (such as attributes and relationships among entities), there are two possible ways, i.e., an extensional description with abstract concepts as topology of the entity concept set, and an intensional description with an entity concept set as topology of the abstract concept set. Although the two description methods are almost identical, an extensional description method provides a holistic view, whereas in an intensional description method entities are constructed from predetermined abstract concepts. Extensional data descriptions are more suitable for CAD systems, because difficult data operations (e.g., modifications) can be done by easy (hence cheap) operations. However, conventional CAD systems are usually implemented based on intensional data descriptions. This is primarily due to good performance for simple data operations. Therefore, a data description method which integrates extensional and intensional views and which satisfies requirements for future CAD systems is needed. The solution is to have two separated worlds, the object world representing entities and the predicate world representing abstract concepts, and functions between them.