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About record structure

Find an overview of the record structure, including content designation and repeatability, of OCLC MARC records.

"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