Ontological considerations about part-of relations have been extensively investigated because they are basic and important relationships for ontology building. Although there are various discussions on kinds of part-of and their ontological characteristics, there remains some room for discussing a couple of fundamental issues such as "What is a part?" and "When is a part-of relation composed?" This paper discusses ontology patterns of descriptions of part-of relationships on the basis of ontological theories in order to provide practitioners with useful guidelines for descriptions of part-of structurers. This paper focuses on ontology patterns which capture commonality and special characteristics of parts so that complicated structures of physical objects are described appropriately. We discuss four problems related to descriptions of parts. 1) interdependence between the whole and its parts, 2) kinds of parts such as components, portions and materials, 3) multiple inheritance according to substance and properties of parts, 4) the commonality and specificity of parts. To cope with these problems, this paper introduces a part representation model based on ontological theory of roles. The main idea of the part representation model is to distinguish between a part dependent on its whole and the context-independent properties of the part. The former is defined as the role-holder which plays roles and the latter is defined as the player of the role. The role defines properties of the part which is dependent on its whole. These three kinds of definitions enable to describe differences of various properties of parts according to their context dependence. We show how this model is used to describe various parts through practical examples of the anatomical structure of human body developed in the medical ontology project in Japan.
SummaryRecently, an ontology is expected to contribute to knowledge sharing and reuse.It is, however, difficult to develop well-organized ontologies because the principles of ontology design are not clear enough. Therefore, a methodology for ontology design and a computer system supporting ontology design are needed. Our research goals include a methodology of ontology design, and development of an environment for building and using ontologies. Building an ontology requires a clear understanding of what can be concepts with what relations to others. An ontology thus focuses on "concepts" themselves rather than "representation" of them. Although several systems for building ontologies have been developed to date, they were not based on enough consideration of an ontological theory. We argue that a fundamental consideration of these ontological theories is needed to develop an environment for developing ontologies. Most of the previous ontologies, which are represented in frame-based languages, don't clearly deal with such concepts that need deep ontological investigation. Therefore we begin with a fundamental consideration of an ontological theory. We discuss mainly "role concept" and "relationship", and consider how these ontologically important concepts should be treated in our environment. On the basis of the consideration we have designed and have developed an environment for building and using ontologies, named "Hozo". This paper presents an outline of the functionality of Hozo. We focus on how it treats the relations and roles on the basis of fundamental consideration.
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