There are two difficulties with subject headings in a library catalog. For one thing, you must know what the subject heading is before you can search on it. For another, not all libraries use the same subject list. At first, it seems worse than the old complaint that you can’t look up how to spell a word in the dictionary unless you know how to spell it.
In the days of card catalogs, patrons had little choice but to make their best guess and hope to find something. College and university libraries, which overwhelmingly use Library of Congress Subject Headings, used to keep the whole list–all four or five volumes of the so-called “Red Books”–out where patrons could use them.
I used them from time to time and never had to stand in line. In fact, most patrons probably did not use them or even know what they were for. The nice thing was that I could make my guess, look in the “Red Books,” and if I was wrong, would very likely find a cross-reference. Unfortunately, the abbreviations for the various kinds of cross-references were devised by librarians for other librarians. They were hard for non-librarians to understand or interpret.
Subject searching is actually better in an online library catalog. All those confusing cross-references in the “Red Books” work invisibly under the hood. When a patron needs them, they appear written in intelligible English. But there is a better way to approach subject searching than just guessing at what a real heading might be.
Various systems of classification
First, though, some background is necessary. Most academic libraries use Library of Congress Subject Headings (LCSH). Most public libraries use Sears List of Subject Headings. Most medical libraries use Medical Subject Headings (MeSH). The Library of Congress issues a separate list of headings for children.
All of these classification systems operate on the same basic principles: For every subject, there is one and only one term used to describe it in the catalog (controlled vocabulary). Terms exist in some kind of hierarchy from the most general to the most specific; the cataloging record for each title will have only the most specific headings. The cross references to a given subject heading may show broader or narrower terms, but there is no way to trace an entire hierarchy.
Although they operate on the same principles, the different systems do not use the same terms. What is the preferred term in one will be invalid in another. For example, “cancer” is a subject heading in both Sears and LCSH, but not in MeSH; the valid heading there is “neoplasms.” If, for example, a university includes a medical school, and if the medical library and other libraries share a single catalog, that catalog must have separate indexes for searching LSCH and MeSH to avoid confusion.
The easiest way to search
The easiest way to find subject headings is to start with a keyword search, using the most specific terms you can think of. Under the influence of search engines, many online library catalogs display only a single search box. That works much less well for a catalog or other database than for a search engine, but it’s a place to start.
If you see a link to “advanced search,” use it. In almost any database, the advanced search is more useful and actually easier to use than the simple search. For subject searching, it may have separate search boxes for subject headings, subject keywords, and general keywords. Enter your terms in subject keywords if available; otherwise choose general keywords.
Your search will return a list of records that contain that term (or, if you have chosen a non-preferred term, records that contain the subject heading). Choose any title that looks promising and click on it to open the record. There, under subjects, you will find the subject heading associated with the keyword you searched, along with any other subject headings in that record. Click on a subject heading and you will get a list of everything in the library with that heading.
In a well designed catalog, a complex subject heading, that is a string of more than one term like “Dogs–United States–Biography–Humor,” will present each term as a separate link. Click on “Dogs” and you should get back a list of subject headings that begin with “Dogs,” followed by screen after screen of all of the subheadings. Click on “United States” and you should get a list of headings that begin with “Dogs–United States,” etc. The farther to the right you click on one of those strings, the more specific search results will return. Unfortunately, not all online library catalogs are well designed.
If you are planning to look up a lot of resources about your subject, write down every useful subject heading you find. You will be able to enter it directly in the search box for subject headings when you return to the catalog and skip the guessing stage.