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About record structure

"Record Structure" describes the general structure for the leader, the directory, and the control and variable fields in OCLC-MARC bibliographic and authority records.

OCLC-MARC format

OCLC-MARC formats are sets of codes and content designators defined for encoding particular types of machine-readable records. They serve as the vehicle for bibliographic and authority data for all types. The formats provide specifications for the exchange of information between systems.

Additional information on OCLC-MARC format

For descriptions of the OCLC-MARC bibliographic and authority records, see Bibliographic Formats and Standards and Authorities: Format and indexes.

Content designation

Content designation identifies and characterizes the data elements that comprise OCLC-MARC records.

Tags and fields

  • OCLC-MARC records are organized into fields identified by three-character numeric tags
  • The tag is stored in the directory entry for the field, not the field itself
  • Fields are grouped into blocks according to the first character of the tag, which generally identifies the function of the data in the record
  • The type of block varies with each type of record: bibliographic or authority

Bibliographic record blocks

Bibliographic records have the following blocks:

  • 0xx Control information, numbers, and codes 1xx   Main entry
  • 2xx Titles and title paragraph 3xx Physical description, etc. 4xx   Series statements
  • 5xx  Notes
  • 6xx   Subject access fields
  • 7xx Added entries other than subject or series; linking fields 8xx   Series added entries, location, and alternate graphics 9xx   OCLC-defined local fields

Authority record blocks

Authority records have the following blocks:

  • 0xx Control information, numbers, and codes 1xx  Heading
  • 2xx   Complex see references
  • 3xx Complex see also references
  • 4xx   See from tracings
  • 5xx   See also from tracings
  • 6xx Reference notes, treatment decisions, notes, etc.
  • 7xx   Heading linking entries
  • 8xx Location and alternate characters
  • 9xx   OCLC-defined local fields


  • All fields are theoretically repeatable
  • The nature of the data in the fields, however, may preclude repetition
  • Examples of nonrepeatable fields include 001 (Control Number), 005 (Data and Time of Latest Transaction), and field 245 (Title Statement)
  • OCLC-MARC Records specifies the repeatability (R) or nonrepeatability (NR) of each field and subfield in the lists of content designators

Coded data

  • OCLC-MARC formats include specifications for data elements represented by coded values
  • Coded values consist of fixed-length character strings
  • Elements within coded-data fields or subfields may be identified by relative character position
  • Although coded data occurs most frequently in the leader, directory, and variable control fields, any field or subfield may be defined for coded data


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