Medical Subject Headings
Features of the MeSH Vocabulary
MeSH contains several different types of terms.
Descriptors (main headings): characterize the subject matter or content.
Qualifiers: are used with descriptors and afford a means of grouping together those documents concerned with a particular aspect of a subject. A list of subheads appears following the list of new descriptors. MeSH also has special types of descriptors that are not printed in Index Medicus but are available for indexing, cataloging, and online searching: Publication Types: characterize what the item is, i.e., its genre, rather than what it is about. Geographics: include continents, regions, countries, states, and other geographic subdivisions. They are listed in category Z of the tree structures.
Entry terms: synonyms or closely related terms that are cross-references to descriptors. Generally, entry vocabulary may be used interchangeably with preferred descriptors for searching of PubMed. Thus, the entry vocabulary is a means by which the MeSH thesaurus can be enriched to the advantage of both the online user and the user of the printed bibliography.
Complex concepts can be described in three different ways. The first of these is coordination, the combined use of two or more separate descriptors. For example, jejunal enteritis may be expressed by the use of Jejunal Diseases + Enteritis. Secondly, qualifiers can be used in conjunction with appropriate descriptors. A deficiency of monoamine oxidase may be indexed as Monoamine Oxidase/deficiency. The direct linkage of the qualifier to the descriptor to which it relates avoids the possibility of false coordination that may occur if two descriptors are used to represent a single concept. Thirdly, many pre-coordinated descriptors are contained in MeSH for frequently encountered subjects. If MeSH has a precoordinated descriptor such as Heart Surgery, the indexer or cataloger uses it rather than a descriptor-qualifier combination. If a descriptor-qualifier combination is available, it will be used in preference to coordinating two descriptors.