Controlled Vocabulary in Library and Information Science
– Controlled vocabulary is a carefully selected list of words and phrases used to tag information units for easier retrieval.
– It solves problems of homographs, synonyms, and polysemes by establishing a clear relationship between concepts and preferred terms.
– Preferred terms are chosen based on user warrant, literary warrant, and structural warrant.
– Controlled vocabularies handle homographs with qualifiers to ensure each term refers to one concept.
– Examples of controlled vocabulary systems include the Library of Congress Subject Headings.
Types of Controlled Vocabulary Tools Used in Libraries
– Subject headings and thesauri are the main kinds of controlled vocabulary tools used in libraries.
– Subject headings describe whole books, while thesauri cover specific disciplines.
– Subject headings tend to have terms in indirect order, while thesaurus terms are always in direct order.
– Subject headings often use pre-coordination of terms, while thesauri use singular direct terms.
– Thesauri list equivalent, narrower, broader, and related terms, while subject headings historically did not.
Indexing Languages
– There are three main types of indexing languages: controlled, natural language, and free indexing.
– Controlled indexing language allows only approved terms for describing documents.
– Natural language indexing language allows the use of any term from the document being described.
– Free indexing language allows the use of any term, even if it’s not from the document.
– Indexers choose the level of indexing exhaustivity, which determines the level of detail in describing the document.
Advantages of Controlled Vocabularies
– Controlled vocabularies improve the accuracy of free text searching by reducing irrelevant items in the retrieval list.
– They eliminate ambiguities caused by the inherent ambiguity of natural language.
– Using controlled vocabulary can significantly increase the precision of an information retrieval system.
– Controlled vocabulary can enhance recall by eliminating the need to search for synonymous terms.
– It improves the performance of information retrieval systems compared to free text searching.
Problems with Controlled Vocabularies
– Controlled vocabulary searches may have unsatisfactory recall, failing to retrieve relevant documents.
– Users must have a deep understanding of the controlled vocabulary to avoid missing relevant documents.
– Low indexing exhaustivity may result in important aspects of a document not being described with index terms.
– Some articles may not be tagged with the correct term if it is considered secondary to the main focus.
– Controlled vocabulary requires expertise and careful selection of terms to address these problems.
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Controlled vocabularies provide a way to organize knowledge for subsequent retrieval. They are used in subject indexing schemes, subject headings, thesauri, taxonomies and other knowledge organization systems. Controlled vocabulary schemes mandate the use of predefined, preferred terms that have been preselected by the designers of the schemes, in contrast to natural language vocabularies, which have no such restriction.
