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What are subject headings?

Titles are often poor indicators of the content of the books to which they belong. For example, what is the topic of the book titled, Have a seat, please? Barbers? Furniture? (It's actually about capital punishment.) What is the topic of the book titled, The view from nowhere? (It's actually a philosophical work about objectivity.)

The lack of a straightforward connection between a work's title and it's content presents a problem for researchers, namely, how can a researcher do a topic search for materials in the library catalog when the search terms he uses might not match anything in the titles of some works on his topic? For instance, no matter what words I might use to reasonably describe the topic "capital punishment," it's unlikely that any of these will match the title, Have a seat, please. So how can I have a chance of retrieving works like this whose titles bear little relationship to their topics?

You probably already guessed the answer to this problem. You can retrieve these books by matching your search terms with the words in the subject headings of their library catalog records, indicated in the library catalog's records by the phrase, "Subject term."

Knowing more about subject headings will enable you to use them more effectively for your research and will make you a better researcher.

One question to consider regarding subject headings is, who decides which subject headings apply to each book? The author? The publisher? Actually, in most cases, it is the Library of Congress.

The Library of Congress reviews works published in print and determines which subject headings apply to these works.

Even more than deciding which subject headings apply to particular books, the Library of Congress also determines the vocabulary of the subject headings. This is important because there is no duplication of topics in subject headings. That is, the English language allows for more than one way to represent a particular topic. For instance, "Death penalty" and "Capital punishment" basically represent the same topic. Similarly, "Metropolitan hospitals" and "Urban hospitals" also represent the same topic, as do "Iron casting" and "Iron founding." But in order to improve the efficiency of subject headings, whenever there is more than one way to represent a topic in ordinary language, the Library of Congress chooses only one of those ways to be the official subject heading. So, for example, it chooses "Capital punishment," "Urban hospitals," and "Iron founding," and rejects "Death penalty," "Metropolitan hospitals," and "Iron casting."

The terms that the Library of Congress has selected as its official subject headings are published in a number of large red volumes. These have to be updated regularly to account for changes in common usage and additions to the language. (For instance, the headings "Laptop computers" and "MP3 players" didn't exist 30 years ago.)

Because Library of Congress Subject Headings (or LCSH's) don't allow for repetition of topics and have strict rules for being changed or added to, this set of terms is called a controlled vocabulary.

How to find subject headings

Due to the fact that the Library of Congress Subject Headings vocabulary is a a controlled vocabulary, in order to use it to research a particular topic, you need to find how the topic is represented in the Library of Congress's terminology.

How does one go about doing this? Actually, there are a few ways.

Let's consider an example. Suppose I want to find how the topic "Ergonomics" (which is the science of equipment design for the workplace for the purpose of reducing worker fatigue and discomfort) is represented in the Library of Congress's Subject Heading terminology.

First, you can look up "Ergonomics" in the Library of Congress Subject Headings Red Books. For "Ergonomics," the Red Books say, "USE Human Engineering." This means that the official Library of Congress Subject Heading for the topic of ergonomics is "Human engineering."

Another option (which you might use if you didn't have the Library of Congress Subject Headings Red Books at your fingertips) is to enter your topic into a "subject" search in the Library Catalog using the "Browse" option.

After clicking on the "search" button, the catalog indicates, "see related headings for: Ergonomics."

If you then click on the link for "Ergonomics," you will find that the catalog advises to "search under: Human engineering." This tells us (as in the Red Books) that the official Library of Congress Subject heading for ergonomics is "Human engineering."

Finally, you could enter "Ergonomics" into a title keyword search in the Library catalog.

Then, on the resulting retrieval list, search for a record that clearly seems, based on its title, to be about this topic.

Then click on the "Details" of the record. You can then scan the subject headings in the record to find the subject heading assigned by the Library of Congress to represent this subject. If you do this, you will see, again, that the Library of Congress represents this topic with the phrase, "Human engineering."

Using subject headings

What good does it do to find that, for example, the official LCSH for "Ergonomics" is "Human engineering"? Well, once you have found the Library of Congress Subject Heading that represents your topic, you can use it in various ways to help your research. For instance, you can enter it in a subject search in keyword mode. This search will find every record in the Library catalog that has this phrase in its subject headings.

(Notice that the subject phrase you enter should be flanked by single quotation marks, for example: 'human engineering'. This is the punctuation that should be used to search these words as a phrase in the Library catalog, i.e. only retrieving records that have these words together and in just this order.)

The great thing about using a LCSH in this way is that every item on the list of items retrieved will be about your topic, and most, if not all, of the items in the Library on your topic will be on this list. This is basically what the good researcher wants to do when searching in a database: find all the items that are relevant to his topic (so he doesn't miss anything good) and find only the items that are relevant to his topic (so he doesn't have to sift through a lot of irrelevant records). In short, using Library of Congress Subject Headings in this way is a very efficient way to do your research on a particular topic.

In viewing some of the records retrieved with this search, you might also find that there are interesting combinations of subjects. For instance, you might find a record that combines two topics you find interesting, human engineering and aeronautics

You can then take both of these terms, "Human engineering" and "Aeronautics," and enter them in a subject keyword search joined with the word "and." This search will retrieve all of the Library's records with both of these terms in their subject headings, providing you with most, if not all, of the Library's materials on this combined topic.

Another way to use a Library of Congress Subject Heading is to enter it in a subject Browse search. (Note: For "Browse" and "Exact" search modes, there is no need to use single quotation marks to keep words togther as a phrase. These search modes automatically treat the words you enter as a phrase.)

In this way, you can display all the subject heading "strings" that begin with the subject heading you entered.

Then, for instance, if you want to select all of the records that contain your subject as the entire line, without any qualifications, you can click on that link on the list. Note that this is equivalent to doing an Exact subject search of "human engineering".

You can also browse through the list retrieved by a Browse subject search to get ideas for narrowing your topic. For instance, you might run across the subject heading line "Human engineering--Government policy--United States" and decide that you want to pursue this particular topic. You can navigate through the "Browse" retrieval list by using the "Previous" and "Next" buttons at the top of the page.

You also may have noticed that the subject heading lines in Library catalog records (preceded by the phrase "subject term") are hot links. Clicking on these links is another way to use LCSH's.

Clicking on a subject heading link will retrieve all the records in the catalog that contain a "Subject term" line that has exactly the subject heading you have clicked on. Of course, any record you retrieve may, and probably will, have other Subject term lines as well. Clicking on a link just guarantees that you will retrieve all the records that have at least one Subject term line with exactly the same heading as the one you clicked on.

Clicking on a subject heading link in a record is equivalent to entering the subject heading in an Exact subject search in the catalog. That is, these two searches will retrieve exactly the same set of records.

Finally, a word of caution. As great as the Library of Congress Subject Headings are for assisting research, you shouldn't depend on them exclusively. Sometimes the Library of Congress makes surprising decisions as to whether a work is about a particular topic, and sometimes it's simply the case that mistakes are made when subject headings are applied to catalog records. To make sure you aren't missing any items in the Library catalog that are relevant to the topic you are researching, you still should use Boolean keyword searching with non-LCSH terminology in addition to LCSH terminology. For instance, staying with the topic of ergonomics, it would be a good idea to begin your research with a keywords anywhere Boolean search that includes the term "ergonomics" as well as its corresponding LCSH: ergonomics or 'human engineering.'

Doing library research is not an exact science, but the more tools you have and the better you know how to use them, the better chance you have of doing effective and efficient research. The Library of Congress Subject Headings are just such a tool.

Reference

Mann, Thomas, "Teaching Library of Congress subject headings," Cataloging & Classification Quarterly, v.29, no.1/2 (2000), pp.117-26.

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