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Control and variable fields

Find the control fields, variable fields, and variable field components for OCLC MARC records.

The control and variable fields consist of variable-length alphanumeric data. They may differ in content for each type of MARC record.

Subfield delimiters and codes separate alphanumeric data within variable fields. No spaces appear before and after subfield delimiters and codes.

All fields end with a field terminator. A field terminator code and a record terminator code follow the last field.

Control fields

Control fields in MARC 21 formats are assigned tags that begin with two zeros.  

  • They contain data and a field delimiter
  • They do not contain indicators or subfield codes
  • The control number field is assigned tag 001 and contains the control number of the record
  • Each record contains only one control number field (with tag 001), which is located at the base address of data

Variable fields

Variable fields in MARC 21 formats are assigned tags which are ASCII numeric characters and which do not begin with two zeros.

  • Such fields contain indicators and subfield codes, as well as data and a field terminator
  • The number, length, or content other than that already stated or implied, for example, those resulting from the limitation of total record length, if not restricted

Variable field components

Each variable field in a bibliographic or authority record has the following components:

Element Description
Indicator 1 and 2
  • First character positions of a variable data field, preceding any subfield code (delimiter plus data element identifier) which may be present
  • Each data field includes 2 indicators, even if the values have not been defined in a particular field
  • Indicators supply additional information about the field and are defined individually for each field
  • Values are interpreted independently–meaning is not ascribed to the 2 indicators taken together
  • MARC 21 formats use numeric values for indicators
  • A blank is used in an undefined indicator position or means information not provided in the defined indicator position
Subfield code
  • Identifies the individual data elements within the field
  • Precedes the data elements
  • Each data field contains at least one subfield code
  • The subfield code consists of a delimiter [1F 16 , 8-bit] followed by a data element identifier
  • Data element identifiers defined in MARC 21 may be any ASCII lowercase alphabetic or numeric character