Thesauri, subject headings, and keyword searching have been the customary strategies used for the location of materials. Categorizing by subject or descriptor term creates a thesaurus of specified terms, a controlled vocabulary. Glossaries are useful for finding alternative words. Searching indexes and other lists can help to identify cataloged items. Thus, glossaries, subject indexes, and thesauri can be extremely helpful in the reference process. These tools can also facilitate communication between users and librarians. Especially useful are alternative keywords for search terms and the different ways the sites organize their data. The three categories below are not all inclusive, and there is some overlap.