Subject vs. keyword searching

Subject searching and keyword searching are two common ways to search for information in an online database, in a library catalog, or on the Web.  So what's the difference?

SUBJECT SEARCHING uses controlled vocabulary, an agreed-upon word or phrase to describe and define a concept or a thing.  In each system, there is a standardized list of subject terms or codes that the indexers or catalogers use to choose their terms.  These headings can be broad or fairly specific, and terms will vary from one system to another.  Examples of controlled vocabulary include subject headings, descriptors, and classification codes.

• In online databases, indexers assign subjects to magazine and journal articles based on the content of each article. 
• In libraries, catalogers assign subjects to books and other materials to describe what each book is about, and books are arranged on the shelves according to their subjects.  Library catalogs generally use Library of Congress Subject Headings. 
• Some scholarly databases including ERIC, PsycINFO, and Sociological Abstracts use descriptors, another kind of subject term.  
• Some databases use other classification codes relevant to a particular discipline or field of study (numeric classification codes in PsycINFO, SIC or product codes for companies and industries.) 
• On the Web, human indexers for search engines categorize web sites according to particular subjects.

Generally the number of subject terms assigned to a particular item is limited and may not cover the variety and complexity of topics covered by the item.  However, once you find useful subject terms you can eliminate a lot of irrelevant items, since subject searching puts records together by common terms.  Several search engines (Yahoo is perhaps the most famous) classify web sites in broad subject categories and let you narrow your focus step-by-step.

EXAMPLE:  Look up Cabs in the Yellow Pages.  Instead of finding listings under cabs, you will be directed to look under the agreed-upon term taxicabs and other transportation.  This is an example of controlled vocabulary.

KEYWORD SEARCHING will find the word(s) you type anywhere in a record, including the article or document title, the abstract, the subject headings, and the full text if available.  Sometimes you can also search more specifically that way.  However, typing in a single keyword generally retrieves tens or hundreds of thousands of items, most only marginally useful!

Keyword searching is best used when you are not sure of exact subject headings, if you're using "jargon" terms (terms that mean something in a particular field and may not be in general use), or if you aren't getting enough results from a subject search.  Use additional keywords to refine your search; most systems will let you combine terms with "and," "or," and "not" (check the system help.)  When you find a relevant item, check it for any additional keywords that might help your search.  Also be aware that words may have more than one meaning; consider job (as in work) is also Job (the book in the Bible); Turkey is a country as well as a bird.

Some guidelines:

• Put the most important keywords first.
• Use several words, rather than one or two.
• When searching for information about a person, that person is your subject.  Search by the last name, then the first name.
• If the first 20 "hits" or results don't work out, try another approach or another database or search engine.
• Check your spelling.
  

See also:

• Library of Congress Subject Headings

To summarize:

• Using subject headings and other controlled vocabulary lets you search consistently for items related to your topic.
• Keyword searching lets you search for your term(s) anywhere and can result in very broad or very specific searches.