In a traditional library, books and other materials are catalogued and even arranged on the shelves according to their subjects . These are usually fairly broad general topics established by an authority like the Library of Congress.
Periodical indexers assign subjects to magazine and journal articles based on their content.
The number of subject headings is limited, and may not reflect the complexity and variety of topics covered in a particular article. Subject searching can be difficult for students if the category is not obvious. Computerized keyword searching allows you to find more information because the computer looks at words in the titles and content of a source as well as the subject. It also allows you to find more specific information, because each source yields many more keywords than subjects. The challenge in using keyword searching is to refine your topic so that the search yields an adequate number of useful citations.