The variable fields follow the leader and the directory in the record and consist of control fields and data fields.  Control fields precede data fields in the record and are arranged in the same sequence as the corresponding entries in the directory.  The sequence in which data fields are stored in the record is not necessarily the same as the order of the corresponding directory entries.

Control fields:  Control fields in MARC 21 formats are assigned tags beginning with two zeros.  They are comprised of data and a field terminator; 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 to be located at the base address of data.

Data fields:  Data fields in MARC 21 formats are assigned tags beginning with ASCII numeric characters other than two zeros.  Such fields contain indicators and subfield codes, as well as data and a field terminator.  There are no restrictions on the number, length, or content of data fields other than those already stated or implied, e.g., those resulting from the limitation of total record length.  The structure of a data field is shown schematically below.

Structure of a Variable Data Field in MARC 21 Records

Indicators:  These are the first two characters in every variable data field, preceding any subfield code (delimiter plus data element identifier) which may be present.  Each indicator is one character and every data field in the record includes two indicators, even if values have not been defined for the indicators in a particular field.  Indicators supply additional information about the field, and are defined individually for each field.  Indicator values are interpreted independently; meaning is not ascribed to the two indicators taken together.  Indicators may be any ASCII lowercase alphabetic or numeric character, or blank.  A blank is used in an undefined indicator position, and may also have a defined meaning in a defined indicator position.  The numeric character 9 is reserved for local definition as an indicator.

Subfield codes:  These identify the individual data elements within the field, and precede the data elements they identify.  Each data field contains at least one subfield code.  The subfield code consists of a delimiter (ASCII 1F(hex)) followed by a data element identifier.  Data element identifiers defined in MARC 21 may be any ASCII lowercase alphabetic or numeric character.  In general, numeric identifiers are defined for data used to process the field, or coded data needed to interpret the field.  Alphabetic identifiers are defined for the separate elements which constitute the data content of the field.  The character 9 and the following ASCII graphic symbols are reserved for local definition as data element identifiers:

! " # $ % & ' ( ) * + , - . / : ; < = > ? { } _ ^ ` ~ [ ] \

A data field may contain more than one data element, depending upon the definition of the field.  The last character in a data field is the field terminator, which follows the last data element in the field.

To return, select:

Record Structure