1) enable user to find a book when either one of these is known to the user: the author, the title, or the subject.
2) show what the library has by a given author, or on a given subject, or in a give kind of literature.
Authority records contain data like: a unique control number, the preferred terms, the non-preferred terms, the variant form of the terms, the broader/narrower/related terms, scope notes, and supporting reasons of creation of the terms.
Library OPAC provides search by author, subject and title, etc.; in addition to keyword search. In FRBR’s terminology, it provides search by types of entities (Work, Expression, Person, Corporate Body, Family, Concept, Events, Place, Object). Nowadays, OPAC even provides faceted search by these entities and few key parameters derived from fixed fields and other fields of marc.
The success in providing the FINDING and GATHERING function in cataloguing relies on two things. First is the authority control, which is the work of building of authority files that houses the authority records. Second is the bibliographic control, which includes the process of assigning of appropriate terms (access points) from authority file in the bibliographic records (or the metadata). Take the example of the previous post of ‘Haze’ collection, the success of the catalogue requires a some authority control work to re-organise the index terms.
The Library of Congress Name and Subject Authority files are the most widely used controlled vocabularies in libraries worldwide, although they are known to have bias. The two files represent many many great librarians’ contribution to the library communities servicing their customers in more than 100 years. LC Subject Headings sometimes are difficult to use and there are calls to simplify it. FAST is a project trying the tackle this problem.