Controlled vocabulary terms serve to index the contents of books, journal articles and other items in a predictable, standardized way. Controlled vocabulary terms are frequently called subject headings, subject terms, descriptors, or indexing terms . Consider the controlled vocabulary in a source you're undoubtedly familiar with, the Yellow Pages of your local phone directory. In the Yellow Pages example, looking up information in a print source follows a consistent pattern. We will discuss the purpose, advantages, and disadvantages of controlled vocabulary at more length in a future lesson.
Natural language contrasts with the rigid format of controlled vocabulary.
Natural language uses words new to fields and not yet fully accepted because the ideas to which they refer are still too new to be widely accepted. This language also uses words in idiosyncratic, specialized ways by individual writers and researchers and also uses words with shifting meanings over time. Natural language searching of databases is also called freetext searching, as it allows the searcher to search an entire record in the database rather than limiting the search to a specific field.