An Enriched Unified Medical Language System Semantic Network with a Multiple Subsumption Hierarchy
- Affiliations of the authors: CS Department, New Jersey Institute of Technology, Newark, NJ (LZ, YP, JG); Mathematics & ComputerScience Department, Kean University, Union, NJ (MH); Department of Medical Informatics, Columbia University, New York, NY (JJC)
- Correspondence and reprints: Li Zhang, MS, Room 4214, GITC Building, CS Department, NJIT, University Heights, Newark, NJ 07102; e-mail: <lxz1853{at}njit.edu>
- Received 14 October 2002
- Accepted 13 January 2004
Abstract
Objective The Unified Medical Language System's (UMLS's) Semantic Network's (SN's) two-tree structure is restrictive because it does not allow a semantic type to be a specialization of several other semantic types. In this article, the SN is expanded into a multiple subsumption structure with a directed acyclic graph (DAG) IS-A hierarchy, allowing a semantic type to have multiple parents. New viable IS-A links are added as warranted.
Design Two methodologies are presented to identify and add new viable IS-A links. The first methodology is based on imposing the characteristic of connectivity on a previously presented partition of the SN. Four transformations are provided to find viable IS-A links in the process of converting the partition's disconnected groups into connected ones. The second methodology identifies new IS-A links through a string matching process involving names and definitions of various semantic types in the SN. A domain expert is needed to review all the results to determine the validity of the new IS-A links.
Results Nineteen new IS-A links are added to the SN, and four new semantic types are also created to support the multiple subsumption framework. The resulting network, called the Enriched Semantic Network (ESN), exhibits a DAG-structured hierarchy. A partition of the ESN containing 19 connected groups is also derived.
Conclusion The ESN is an expanded abstraction of the UMLS compared with the original SN. Its multiple subsumption hierarchy can accommodate semantic types with multiple parents. Its representation thus provides direct access to a broader range of subsumption knowledge.
