CLASSES AND INSTANCES

Abstract

The power of any information system technology is delimited by the expressiveness of the notation used to represent information. Classification constitutes a fundamental notational structuring mechanism and, not surprisingly, is supported in one form or another by many formal notations intended for data or knowledge modelling. This paper presents an overview of various manifestations of classification mechanisms. Further, characteristic features of classification, such as the form of inheritance allowed from classes to instances, having single or multiple classifications and the structure of the classification hierarchy are identified, discussed, and contrasted. The paper also describes the classification mechanism offered by the knowledge representation language Telos. In Telos, classification is stratified and applicable not only to objects but also to (binary) relationships. The paper argues that these features lead to a more expressive notation, acquired at relatively modest conceptual and computational costs.