한글의학용어의 UMLS 통합

Integrating Korean Medical Vocabulary into the UMLS

Seung-Bin Han*, Jinwook Choi M.D., PhD.* ,William T. Hole, M.D.□, Suresh Srinivasan□

* Department of Biomedical Engineering, College of Medicine, Seoul National University, Seoul 110-799, {sbinhan, jinchoi}@snu.ac.kr, □National Library of Medicine, Bethesda, MD, USA, {wth, suresh}@nlm.nih.gov

Abstract: The UMLS(Unified Medical Language system) is one of the most comprehensive medical terminology systems. We present the problems we faced and their solutions when we tried to add Korean terms to the Metathesarus of the Unified Medical Language System (UMLS MT). Challenges to integrating Korean into the UMLS MT are analyzed, such as matching UMLS terms and concepts, incomplete translation, character set incompatibility, and absence of lexical resources to create Korean indexes. Suggestions are given to improve the integration of Korean terminology into the UMLS. Our work is expected to be a useful precedent to merge medical vocabularies in other languages into the UMLS MT.

Keyword: UMLS, Metathesaurus, Multilinguality, integration, Korean medical vocabulary, electronic medical terminology system,

Ⅰ. INTRODUCTION

Multilinguality is a major issue for the international use of medical terminologies since it is a way to share and reuse knowledge [1]. However, the use of medical knowledge does not always require language-dependent support. Multilinguality is a common feature of all major medical terminologies (UMLS ,ICD[2], GALEN[3],  SNOMED International[4],  ICPC). Controlled terminology is key to the utility of Clinical Patient Record (CPR) systems [5-7]. Despite dramatic developments in medical knowledge and IT technologies in Korea, no Korean language is contained in medical terminology systems, except for ICD. We have therefore made a special effort to include the Korean language (Hangul) in the UMLS Metathesaurus (MT). In this paper, we present the process of integration, problems faced, and solutions for inclusion of Korean into the UMLS.

Ⅱ. BACKGROUND

The goal of NLM's long-term Unified Medical Language System□ (UMLS) project is to help health professionals and researchers use biomedical information from different sources, to facilitate information sharing and to enable accurate transmission of medical data or knowledge [8].

There are three major components in the UMLS Knowledge Sources:

1. The UMLS Metathesaurus□ (MT) :  It is organized by concept or meaning. The 2003AA edition of the MT includes 875,255 concepts and 2.14 million concept names in its source vocabularies.

Two important tables in the MT are used for integration. The MRCON table is composed of several fields. The Concept Unique Identifier or CUI is one key identifier. CUIs connect all names for a given concept, and are used to link concepts in relationships, and identify all attributes of a concept. Lexical Unique Identifiers (LUIs), identify and link all concept names that are lexical variants of each other, and String Unique Identifiers (SUIs), identify and link all identical strings. The string field, STR is used for storing the concepts names. The MRSO table has a source abbreviation field (SAB) and a CODE field for each entry in the source vocabulary and shares the three unique identifiers in MRCON.

2. The Semantic Network, through its semantic types, provides a consistent categorization of all concepts represented in the MT.

3. The SPECIALIST Lexicon (SL) is an English language lexicon with many biomedical terms. Information for each entry includes base form, spelling variants, syntactic category, inflectional variation of nouns and the conjugation of verbs. The tools also identify words and strings used in the Metathesaurus indexes.

Ⅲ. ANALYSIS OF CHALLENGES

We present an analysis of some of the problems encountered in the UMLS when integrating languages other than English especially the Asian languages. The following problems currently limit integration and use of the UMLS in Korean:

What approach is appropriate for adding Korean terms to the UMLS MT: concept level & term level

Since the UMLS MT is composed of concepts and interconcept relationships, in principle, it is a language-independent representation of medical knowledge. However, words are used to name concepts, and, at the term level, the MT is language-dependent. Therefore, we need to evaluate coverage of the UMLS as compared with Korean medical concepts, and to identify differences. Also, we must identify the best way of integrating the Korean medical vocabulary into the UMLS MT at the term level.

Quantitative and qualitative issues related to translation

While UMLS concepts come from more than 100 vocabularies, the UMLS MT has not any Korean terms. MeSH, the Medical Subject Headings, is a comprehensive medical thesaurus which indexes documents in the MEDLINE database [9]. MeSH is a valuable component of the UMLS MT, and many MeSH translations appear in the MT.  Korean librarians have attempted to translate the MeSH since 1995. However, the translations were incomplete because only some Korean terms were included, and it was just translated into a Korean dictionary [10]. A future translation should be done in collaboration with the NLM [11].

Character set incompatibility

The proper representation of Korean characters in MT files is a major issue. The character set used to represent characters in UMLS terms is 7-bit ASCII including transliterated 8-bit characters from a number of Western European languages. The Korean character code systems are based on a 2-byte code systems (DBCS). They use all 16-bits to represent Korean characters in Hangul.  Finally, retrieval and searching across character sets is a difficult problem which will be solved with Unicode [12] and character equivalence tables. Character equivalence tables have yet to be built.  Further, Unicode must be implemented for all users of differing operating systems. Such support is still evolving.

Lexical tools to create the Korean indexes

Lexical matching techniques require lexical items to be identified and transformed into their base form. Then, derived forms can be computed. LVG computes inflectional and derivational variants by applying a set of rules and facts to the base forms [12]. These lexical resources do not currently exist for Korean in the UMLS. Korean language and its rules and facts for variant generation are complicated and very different from other alphabet based languages, so we must develop lexical tools to create the Korean indexes and to assign LUIs to terms in our vocabularies.

Ⅳ. POSSIBLE SOLUTIONS and

The INTEGRATING PROCESS

Adapting Unicode system

We are currently using a KSC5601-1987 character set and a Unicode 2.0 character set in multilingual software. The 11,172 characters are used in most Korean Windows OS systems. There are mapping tables from KSC5601-1992 and others to Unicode 3.0 at www.unicode.org, Unicode 3.0 has the same range as Unicode 2.0, without any changes. To validate the Unicode 3.0, we tested compatibility of character code in different systems. We sent sample files in Metathesaurus format saved as Unicode and UTF-8 to the NLM where it was determined that the files and characters were correctly represented. We must note that not all computer systems or applications currently support Unicode characters.

Approach determination for integration

In order to determine what approach is appropriate to integrate Korean terms in the UMLS MT between the concept and term levels, we estimated the concept coverage and capability of the UMLS as proposed for its application into the CPR system in Korea. As a preliminary study, we examined how many concepts in the current UMLS can cover the existing clinical terms presently used in the Korean medical records. To do so, we tested the mapping between □chief complaints□ extracted from the discharge records of Seoul National University Hospital (SNUH) and the UMLS □Sign or Symptom□ concept terms. Thirty-five percent of chief complaints of the SNUH were conceptually matched with the UMLS □Sign or Symptom□ concepts. Most of fifth-eight percent were matched with □Disease or Syndrome□ concepts of UMLS rather than matched with □Sign or Symptom□ concepts of UMLS MT. The rest terms of seven percent were not found in the UMLS MT or those terms that used to special circumstances of a tertiary hospital in Korea.

Fig 1.  Concept coverage of the UMLS compared with Korean medical concepts

93% of the Korean medical concepts were covered by UMLS. (Figure 1) We presented an analysis of some of the differences between the two terminology sets and the issues requiring consideration for integration in a study presented at 2002 AMIA annual conference. [14, 15] Finally, we decided to process the Korean vocabularies into UMLS MT at the term level rather than at the concept level rather than to add or create new concepts in MT.

Adding Korean terms in the UMLS MT

The easiest way to rapidly add Korean terms to the UMLS is to merge the Korean translation of a vocabulary which already exists in the MT in English. Unlike merging a new English vocabulary, integrating a translation of a vocabulary already in the MT is usually less challenging than integrating a new terminology because it is integration at the term level and not at the concept level. As first step in integrating Korean medical vocabulary into the UMLS MT, the Korean version of ICD-10 (KCD) was chosen since the KCD has the very same structure as the English one.

For example, the ICD code for Addison's disease is E27.1. Searching for 'E27.1' in MRSO retrieves several strings, all attached to the same concept:

The key combining the first three fields (CUI, LUI and SUI) can be used to join with the MRCON table, for example:

If the Korean string for 'Primary adrenocortical insufficiency' is <원발성 부신피질 기능부전>, and its code is still E27.1, new term and string identifiers need to be created for this string, but no concept identifier, since the concept already exists. The result would be like follows:

We have received the ranges for the SUIs and LUIs for Korean strings from the NLM. There is room for 100,000 of each: SUI range: S + 7 digits ranging from 9900000 - 9999999, i.e. S9900000 - S9999999, and similar LUI ranges. We are free to assign our own unique identifiers SUI, LUI for Korean language, and link them to the universal Concept Unique Identifiers, CUIs.

Figure 2 shows a simplified implementation. In this manner, Korean strings would become synonyms of the corresponding concepts in the MT, and be stored, as all other strings in the MRCON and MRSO table.

Fig 2. Table joining with ICD10 code and the result tables combined with Korean terms

Ⅴ. DISCUSSION

This paper described four major challenges and the integration process when we tried to add Korean terms into the UMLS MT. The process of integration and its possible solutions were based on the suggestions of UMLS staff of NLM through the exchange of much e-mail since 2001 and the meeting at the 2002 AMIA conference. Integration of Korean into UMLS MT is under way. Most of problems and solutions proposed in this paper could be applied to other non-English languages as well--especially Asian languages.

AKNOWLEDGEMENT

We gratefully acknowledge Dr. William T. Hole, Suresh Srinivasan and Olivier Bodenreider (UMLS staff, NLM) for supporting us sincerely.

Our work is sponsored by the Ministry of Health and Welfare in Korea.

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[12] The Unicode Consortium. The Unicode Standard, Version 3.0 www.unicode.org

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