In the article “Specific and Generic Subject Headings: Increasing Subject Access to Library Materials,” Marshall summarizes the advantages and disadvantages to specificity for subject headings. Though there are several advantages, problems occur when very specific subject headings hinder efficient searches. Catalogers also find problems with consistently assigning broader subject headings to those very specific ones. Two different catalog are analyzed in this article: dictionary catalog which does well with specific subject headings, and a class catalog grouping works under broad headings.
Charles Cutter introduced the notion of specific entries of subject headings in his 1904 Rules for a Dictionary Catalog. He stated that a work should not be under the heading of a general class, but under its subject heading. A. C. Foskett thinks Cutter actually meant that to be direct entry, not specific entry. An indirect entry can be equally as specific as a direct entry though, such as “Cats” as a direct entry in a dictionary catalog, and “Domestic animals-cats” as the indirect entry in a classed catalog. The difference is the access point – entering through a broader term or through a specific term. An advantage of entering through a broader term is that an indirect, classed catalog entry will have the “see also” reference for mapping, where the direct-entry dictionary catalog does not. A subject heading that expresses the concept of the work exactly is called being coextensive to the work, or scope-matching. If the subject heading encompassed the coextensive subject heading as well as other related subjects, this would be no longer be specific, but a broader heading for that work.
Specificity of a term is thought of in multiple ways. Some think of it as relative to the other terms in the same indexing language – up or down the level of the language makes the specificity broader or narrower. Others think of is in terms of frequency of use. If a collection grows large enough for a specific subject heading to be searched for multiple times, the term it’s no longer specific in terms of the number of results its subject heading with give a user. Yet another way of thinking of specificity is on how desirable the term is to users.
Specificity is used to satisfy multiple needs in retrieval. When a user searches a subject heading multiple times, it has a high recall rate, but may have several irrelevant works pulled with them to sort though. A search term that resulting in less results, but all works being relevant, has high precision. High precision as the result of specific subject headings is highly valuable to researchers, which saves them time and effort. Specific subject headings also prevent excessive recall (results listed) when a broader heading is searched.
There are also disadvantages to having specific subject headings. Where researchers have very narrowly-focused searches, the general public tends to search more broadly. If they search for a broad term, it would only result in the works that have the broad heading and they would miss out on all the specifically headed works that may be of relevance to them. The argument could be seen the other way as well: Putting both broad and narrow subject headings could be an inconvenience to both the narrow and broad searcher by both types intermingling in search results, giving a very large recall to sift through. Related works should still be gathered together in a catalog for generalists. The Subject Cataloging Manual: Subject Headings give instructions to assign both types of headings in certain subject areas. The Library of Congress Subject Headings (LCSH) give instruction on assigning a primary subject heading with other subdivisions under the headings (i.e. “Topic-Subdivision(s)”). Use of “see also” references could also lead users to other, similar search terms.
Do libraries have both the dictionary catalog and the class catalog when a patron is searching their library’s online catalog? Considering the advantages of both, there are valid points for having specific subject headings, as well as a separate group heading on a hierarchy leveling field, similar to LCSH. There are some items on specificity that seemed a stretch to go with such as specificity being relative to frequency of how many other documents have its same term or specificity in terms of desirability – that no longer even deals with how the term relates to the work, so is absurd to think this would be considered. In the end, specificity is relative to its work, and how detailed it will be depends on the catalogers and the rules they must go by. Must they stick with the controlled vocabulary when choosing a heading? There is no perfect balance to be had yet on results gotten by a search of a user. As much as we would like for our searched to recall exactly what a user wants, many times the issue is actually the user entering terms that aren’t exactly what they’re looking for. Since they themselves may not know exactly what they want, it is important to keep broader, as well as narrower headings.