Page 119 - DLIS405_INFORMATION_STORAGE_AND_RETRIEVAL

Information Storage and Retrieval

Notes 4. Various types of semantic relationships may be identified among the terms in a ...... .

5. Accessing literary warrant involves consulting reference sources such as dictionaries or
textbooks as well as ...... .

12.1 Methodology
In library and information science controlled vocabulary is a carefully selected list of words and
phrases, which are used to tag units of information (document or work) so that they may be more
easily retrieved by a search. Controlled vocabularies solve the problems of homographs, synonyms
and polysemes by a bijection between concepts and authorized terms. In short, controlled vocabularies
reduce ambiguity inherent in normal human languages where the same concept can be given different
names and ensure consistency.
For example, in the Library of Congress Subject Headings (a subject heading system that uses a
controlled vocabulary), authorized terms — subject headings in this case — have to be chosen to
handle choices between variant spellings of the same concept (American versus British), choice
among scientific and popular terms (Cockroaches versus Periplaneta americana), and choices between
synonyms (automobile versus cars), among other difficult issues.
Choices of authorized terms are based on the principles of user warrant (what terms users are likely
to use), literary warrant (what terms are generally used in the literature and documents), and
structural warrant (terms chosen by considering the structure, scope of the controlled vocabulary).
Controlled vocabularies also typically handle the problem of homographs, with qualifiers. For
example, the term “pool” has to be qualified to refer to either swimming pool, or the game pool to
ensure that each authorized term or heading refers to only one concept.

There are two main kinds of controlled vocabulary tools used in libraries: subject
headings and thesauri.
While the differences between the two are diminishing, there are still some minor differences.
Historically subject headings were designed to describe books in library catalogues by cataloguers
while thesauri were used by indexers to apply index terms to documents and articles. Subject
headings tend to be broader in scope describing whole books, while thesauri tend to be more
specialized covering very specific disciplines. Also because of the card catalogue system, subject
headings tend to have terms that are in indirect order (though with the rise of automated systems
this is being removed), while thesaurus terms are always in direct order.
Subject headings also tend to use more pre-coordination of terms such that the designer of the
controlled vocabulary will combine various concepts together to form one authorized subject heading.
(e.g., children and terrorism) while thesauri tend to use singular direct terms. Lastly thesauri list
not only equivalent terms but also narrower, broader terms and related terms among various
authorized and non-authorized terms, while historically most subject headings did not.

The Library of Congress Subject Heading itself did not have much syndetic structure
until 1943, and it was not until 1985 when it began to adopt the thesauri type term
“Broader term” and “Narrow term”.

The terms are chosen and organized by trained professionals (including librarians and information
scientists) who possess expertise in the subject area. Controlled vocabulary terms can accurately

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