Controlled Vocabulary Indexing
In indexing journals offering broad coverage of general medicine and specialties and in indexing sets of periodicals issued by different publishers, indexers usually rely on the external authority of a controlled vocabulary. Controlled vocabularies allow indexers to resolve variances in natural language systematically. The vocabularies establish preferred terms with cross-references from alternative forms of entry. Thus, all relevant references can be gathered under a single heading. Controlled vocabularies also establish hierarchical relationships among related terms. Such hierarchies most often take the form of a thesaurus in which narrower terms are entered as subentries beneath the broader terms to which they relate. The following example is abbreviated from the National Library of Medicine’s Medical Subject Headings (MeSH)12(D:12):
Intercellular Signaling Peptides and Proteins
In using a controlled vocabulary, entry style should follow that of the vocabulary list or thesaurus, not the text.13 Adapting controlled vocabularies too freely for local use may result in indexing that will not be fully functional in electronic systems. Indexable terms not listed in the thesaurus (including proper nouns such as the names of people and institutions) may be added as informal identifiers either in a separate field of a database record or appropriately tagged among the controlled vocabulary terms.13 For example, in an index based on the MeSH vocabulary, an article entitled “Effects of Bilateral Posteroventral Pallidotomy on Subjects With Parkinson Disease” may be indexed under the non-MeSH term “Pallidotomy.” This term, however, should be separated from the controlled vocabulary descriptors in the index record or tagged as a local term to distinguish it from MeSH descriptors. The inclusion of local terms in this way allows for valid additional points of access without compromising the integrity of the formal vocabulary and its hierarchy.
Most indexing and abstracting services base their indexing on controlled vocabularies. Controlled vocabularies are also used among descriptive elements called meta-data, which allow digitized information to be networked in a variety of applications. MeSH is the most comprehensive controlled vocabulary in medicine and is used to index MEDLINE. Other biomedical controlled vocabularies and thesauri include The National Cancer Institute Thesaurus (http://nciterms.nci.nih.gov/www.cinahl.com/).
Even when indexing is based on the language of the text, as in back-of-the-book indexing, MeSH and specialized thesauri may be consulted along with standard medical dictionaries as sources of authority for forms of entry and cross-referencing and as general guides to the language and organization of medicine and its related fields. The MeSH is revised annually and is available both in printed volumes and online from the National Library of Medicine.12
A suggested reference on the subject of controlled vocabularies is Vocabulary Control for Information Retrieval.14