Although theoretically, any piece of information on a given book is amenable to authority control, catalogers typically focus on authors and titles. Subject headings fulfill a function similar to authority records, although they are usually considered separately.
The most common way of enforcing authority control in a bibliographic catalog is to set up a separate index of authority records, which relates to and governs the headings used in the main catalog. This separate index is often referred to as an "authority file." It contains an indexable record of all decisions made by catalogers in a given library (or -- as is increasingly the case -- cataloguing consortium), which catalogers consult when making, or revising, decisions about headings.
It is to be remembered that the function of authority files is essentially organizational, rather than informational. That is to say, they (ideally) contain a sufficient amount of information to establish a given author or title as unique, while excluding information that, while perhaps interesting to a reader, does not contribute to this goal.
Although practices certainly vary internationally, in the English-speaking world, it is generally the case that a valid authority record must contain:
Heading refers to the form of name (or title) that the cataloguer has chosen as the authorized form.
Cross references are other forms of the name (or title) that might appear in the catalog. There are two types of cross-references: see references, which reference forms of the name (or title) that have been deprecated in favor of the authorized form; and see also references, which point to other forms of the name (or title) that are authorized. See also references are most commonly used to point to earlier or later forms of a name (or title).
Statement(s) of justification: In addition to providing a heading and applicable references, a valid authority record should also contain a reference to whatever sources of information the cataloguer used to determine both the authorized and any deprecated forms of the name. This is usually done by citing the title and publication date of the source, the location of the name (or title) on that source, and the form in which it appears on that source.
An example authority record, for author Flann O'Brien, taken from the United States Library of Congress authorities files, is reproduced below. (The original record has been abbreviated somewhat for clarity):
O’Brien, Flann, 1911-1966
Na Gopaleen, Myles, 1911-1966
Na gCopaleen, Myles, 1911-1966
His At Swim-Two-Birds ... 1939.
His The best of Myles, 1983: CIP t.p. (Myles na Gopaleen (Flann O’Brien))
His Myles away from Dublin, 1985: t.p. (Myles na Gopaleen (Flann O’Brien) selection from the
column written for ... under the name of George Knowall)
Rhapsody in Stephen’s green, 1994: t.p. (Flann O’Brien (Myles na gCopaleen))
This example contains all the elements of a valid authority record: the first heading is the form of the name that the Library of Congress has chosen to be authoritative. In theory, every record in the catalog that represents a work by this author should have this form of the name as its author heading. What follow immediately below is a set of see references. These forms of the author's name will appear in the catalog, but only as transcriptions, not as headings. If a user queries the catalog under one of these variant forms of the author's name, she would receive the response: "See O’Brien, Flann, 1911-1966." (See also references, which point from one authorized heading to another authorized heading, are exceedingly rare for personal name authority records, although they often appear in name authority records for corporate bodies.) The final four entries in this record constitute the justification for this particular form of the name: it appeared in this form on the 1939 edition of the author's novel At Swim-Two-Birds, whereas the author's other noms de plume appeared on later publications.
The act of choosing a single authorized heading to represent all forms of a name is often difficult, sometimes arbitrary and on occasion politically sensitive. An alternative is the idea of access control, where variant forms of a name are related without the endorsement of one particular form. See Linda Barnhart's Access Control Records: Prospects and Challenges from the 1996 OCLC conference 'Authority Control in the 21st Century'.
Before the advent of digital OPACs and the Internet, the work of creating and maintaining a library's authority files was generally carried out (if at all) by individual cataloguing departments. This meant that there could be a fair amount of disagreement among libraries over which form of a given name was considered authoritative; so long as a library's catalog was internally consistent, differences between catalogs didn't much matter.
However, even before the Internet revolutionized the way libraries go about cataloguing their materials, catalogers began moving toward the establishment cooperative consortia, such as OCLC and RLIN in the United States, in which cataloguing departments from libraries all over the world contributed their records to, and taking their records from, a shared database. This development gave rise to the need for national standards for authority work.
In the United States, the primary organization for maintaining cataloguing standards with respect to authority work operates under the aegis of the Library of Congress, and is known as the Name Authority Cooperative Program, or NACO