Controlled vocabulary search vs. keyword search

Before we start talking about subject heading search vs. keyword search, let's define subject headings first.

Subject Headings or subjects are a set of standard terms (controlled vocabulary) that are preselected and used by the indexers of a database or a catalog to describe a subject so that it can be easily found.We may use a lot of words for the same topic and that makes searching difficult. Controlled vocabulary or Subject Headings help to bring together under a single word or phrase, all the material that is available on a particular topic.

For example, you find material on both bulimia and anorexia under the subject heading of "Eating Disorders".

The advantage of using subject headings is that the results are usually more relevant to your topic but the trick is to find the correct subject headings which is sometimes not so easy. For example, if you look for Taxi or Cab in the Yellow Pages, you will find nothing. This is because taxis and cabs are listed under "Car Services" which is a subject heading and you have to know this before you can find the list.

One way of finding an appropriate subject heading is to start with a keyword search. Once you found an article or book that seems close to your topic, check out the subject headings listed for it on the main record. Then try your search again with those subject headings.

Keywords are natural language words we use every day. In contrast to controlled vocabulary, keywords are flexible and can be combined in different ways, but they may also bring up a lot of irrelvant searches for you. When you do a keyword search the computer looks everywhere for that word, whether in the full text of the document or the title of it. This is why you get more hits but that does not mean that your results are necessarily better.