MARC 21  is an implementation of the American national standard, Information Interchange Format (ANSI Z39.2) and
its international counterpart, Format for Information Exchange (ISO 2709). These standards specify the requirements for a generalized interchange
format that will accommodate data describing all forms of materials susceptible to bibliographic description, as well as related information such as authority,
classification, community information, and holdings data. The standards present a generalized structure for records, but do not specify the content
of the record and do not, in general, assign meaning to tags, indicators, or data element identifiers. Specification of these elements are provided by particular
implementations of the standards. The MARC formats are defined for five type of data, in particular for data listed below:
The MARC 21 formats are communication formats, primarily designed to provide specifications for the exchange of bibliographic and related information between systems.
They are widely used in a variety of exchange and processing environments. As communication formats, they do not consent internal storage or display
formats to be used by individual systems.
- Bibliographic Data: contain format specifications for encoding data elements needed to describe, retrieve, and control various forms of bibliographic material.
It is an integrated format defined for the identification and description of different forms of bibliographic material. MARC 21 specifications are
defined for books, serials, computer files, maps, music, visual materials, and mixed material.
- Holdings Data: contain format specifications for encoding data elements pertinent to holdings and location data for all forms of material.
- Authority Data: contain format specifications for encoding data elements that identify or control the content and content designation of those
portions of a bibliographic record that may be subject to authority control.
- Classification Data: contain format specifications for encoding data elements related to classification numbers and the captions associated with them.
Classification records are used for the maintenance and development of classification schemes.
- Community Information: provide format specifications for records containing information about events, programs, services, etc. so that this information
can be integrated into the same public access catalogues as data in other record types