Acquisition of Medical Knowledge : Using UMLS in the Conceptual

The use of a taxonomy, such as the concept type lattice (CTL) of Conceptual Graphs, is a central structuring piece in a knowledge-based system. The knowledge it contains is constantly used by the system, and its structure provides a guide for the acquisition of other pieces of knowledge. We show how UMLS can be used as a knowledge resource to build a CTL and how the CTL can help the process of acquisition for other kinds of knowledge. We illustrate this method in the context of the Menelas natural language understanding project. INTRODUCTION Taxonomies and hierarchies are widely used in medical knowledge based systems 1, 2]. Some knowledge representation formalisms indeed give a central place to is-a hierarchies. In particular, the Conceptual Graph (CG) formalism 3] is organized around a central Concept Type Lattice (CTL). The CTL provides the basic concept vocabulary that all domain descriptions will be built of. It is shared by the diierent knowledge sources of the system. Its hierarchical structure determines the valid operations on knowledge representations. The issue is then to build this CTL. UMLS 4] is a repository of a large body of medical knowledge, and its semantic network 1] can be used as a resource for this purpose. However, UMLS is still limited in its coverage 5, 6], and must be adapted to speciic needs. The CTL built using UMLS can then further help the process of acquisition for other kinds of knowledge. We illustrate this method in the context of the Menelas natural language understanding project. This paper is organized as follows. First, we start with a brief recall of basic notions and related literature. Second, we describe the structuration of knowledge in Menelas, and the way it rests on a CTL. Third, we show how UMLS has been used to initiate CTL building, then illustrate how the CTL structures the knowledge acquisition process. Finally, we discuss the advantages and further issues associated with this approach.