Descriptor
The concept
'descriptor' is today mainly used about
assigned controlled terms (cf.,
controlled vocabulary), typically taken from a
thesaurus. (Opposite:
Identifier a kind of assigned non-controlled term).
The term was introduced in Information Science by Calvin
Mooers
in 1950. Calvin Mooers had a theory about descriptors which he later on
(Mooers, 1972) characterized in the following way: "As an intellectual technique
for use by the library profession, the descriptor method was a failure. It was a
failure for the simple reason, that documentalists were incapable of
understanding or practicing the method".
“For a given homogeneous user population, it was found empirically that a relatively small repertory of descriptors could be used together in unlimited combinations to provide the kind of retrieval discriminations needed for selection on actual collections of documents. A typical adequate repertory of descriptors was found to number between 200 and 400 descriptors. Such a small number of descriptors was found—surprisingly enough—to be able to exhaust almost all of the retrieval discriminations that a specified target user population wanted to make. On a pragmatic basis, it was found that adding a greater number of descriptors—allegedly to ‘‘improve the discrimination’’— would actually decrease the utility for retrieval.”(Mooers, 2003, p. 814).
Mooers did not see his own descriptor system as a thesaurus. Actually, he saw a conflict between his own system and thesauri:
“It is found that something less than 100 hours of working time, divided among the members of the working group, suffices to develop a descriptor system for even complex fields of science or technology. This brief set-up time is in startling contrast to the many thousands of hours that have been absorbed in the development of the various thesaurus-based systems for retrieval. It is usually claimed that these thesauri are based on descriptor methods, but they are not. Rather than having a focus upon ideas, they are best characterized as being alphabetized, cross-referenced lists of mere words and terms as found in documents” (Mooers, 2003, p. 815).
Nonetheless are descriptors still widely used in bibliographical databases.
Literature:
Eddison, B. & Batty, D. (1988). Words, words, words—descriptors, subject headings, index terms. Database 11(6), 109-113.
Mooers, C. N. (1972/2003). Descriptors. IN: Encyclopedia of Library and Information Science. Ed. by Allen Kent & Harold Lancour. Vol. 7. New York: Marcel Dekker. (Pp. 31-45). (Reprinted in the 2003 edition of the same work).
Birger Hjørland
Last edited: 28-08-2007