Italicized terms found within definitions are terms for which definitions are also provided.

base address of data

A data element in the leader which specifies the first octet of the first variable field in the record and is equal to the sum of the lengths of the leader and the directory, including the field terminator at the end of the directory.

bibliographic level

A data element in the leader of bibliographic records which provides additional information about the characteristics and components of the record, and is used in conjunction with the type of record data element of the leader.

blank (SP)

ASCII character 20(hex) (represented graphically in MARC 21 documentation as or # ), which is used in indicators and data elements containing coded values (and occurs in data content).  Generally, blank stands for "undefined," but in some instances it has been assigned a meaning.  ASCII name is space.

character

A member of a set of elements used for organization, control, or representation of data.  In MARC 21, a character may be encoded using one or more than one octet, depending on the character set.  All ASCII characters are encoded using one octet in the ASCII encoding and the Unicode UTF-8 encoding, thus a character is equivalent in length to an octet when an element's values are restricted to ASCII.

content designation

The codes and conventions established explicitly by MARC 21 to identify and further characterize the data elements within a record and to support the manipulation of that data.

control field

A variable field containing information useful or required for the processing of the record.  Control fields are assigned tags beginning with two zeros.  Control fields with fixed length data elements are restricted to ASCII graphics.

control number

An ASCII graphic character string uniquely associated with a record by the organization transmitting the record and located in a specific variable field.

data element

A defined unit of information.

data element identifier

A one-character code used to identify individual data elements within a variable field.  The data element may be any ASCII lowercase alphabetic, numeric, or graphic symbol except blank.

data field

A variable field containing bibliographic or other data.  Data fields are assigned tags beginning with characters other than two zeros.  Data fields contain data in any MARC 21 character set unless a field-specific restriction applies.

delimiter

ASCII control character 1F(hex) (represented graphically in MARC 21 documentation as $ or ), which is combined with a data element identifier to make up the subfield code which precedes each individual data element within a variable field.  The ASCII name for the delimiter is unit separator (US).

directory

An index to the location of the variable fields (control and data) within a record.  The directory consists of entries.

encoding level

A data element in the leader of authority, bibliographic, classification, and holdings records which provides information about the fullness of the information and/or content designation in the record.

entry

A field within the directory which gives the tag, length, and starting character position of a variable field.

entry map

A data element in the leader which specifies the structure of the entries in the directory.  Always set to 4500 in MARC 21 records.

field

A defined character string that may contain one or more data elements.

field terminator (FT)

ASCII control character 1E(hex) (represented graphically in MARC 21 documentation as FT or ^ ), which is used to terminate the directory and each variable field within a record.  ASCII name for the field terminator is record separator (RS).

fill character

ASCII graphical vertical bar ( | ) (7C(hex)), which fills a required character position and has the meaning "no attempt has been made to code."

fixed field

A field whose length does not vary.  The term is occasionally used to refer to variable control fields, especially those that contain coded data such as fields 007 or 008.

identifier length

See subfield code length

indicator

A data element associated with a data field that supplies additional information about the field.  An indicator may be any ASCII lowercase alphabetic, numeric, or blank.  Indicators are not used in control fields.

indicator count

A data element in the leader which contains the number positions reserved for indicators in each variable data field.  The indicator count is always set to 2 in MARC 21 records.

leader

A fixed field that occurs at the beginning of each record and provides information for the processing of the record.

length

A measure of the size of a data element, field, or record and is expressed in number of octets.

logical record length

A data element in the leader which contains the length of the entire record, including itself and the record terminator.

octet

A string of 8 bits.  In some cases (e.g., ASCII) each octet represents a character; in other cases (e.g., Unicode) multiple octets may represent a character.

record

A collection of data elements describing or identifying one or more units treated as one logical entity.

record length

See logical record length

record status

A data element in the leader which indicates the relation of the record to a file (e.g., new, updated, etc.).

record terminator (RT)

ASCII control character 1D(hex) (represented graphically in MARC 21 documentation as RT or \ ), which is used as the final character of a record, following the field terminator of the last data field.  ASCII name for the record terminator is group separator (GS).

space

See blank

starting character position

The position, relative to the base address of data, of the first octet of the first character in the variable field referenced by the entry.  The first character of the first field following the directory is numbered 0.

status

See record status

subfield code

The two-character combination of a delimiter followed by a data element identifier.  Subfield codes are not used in control fields.

subfield code length

A data element in the leader which contains the sum of the lengths of the delimiter and the data element identifier used in the record.  Always set to 2 in MARC 21 records.

tag

A three-character string used to identify or label an associated variable field.  The tag may consist of ASCII numeric characters (decimal integers 0-9) and/or ASCII alphabetic characters (uppercase or lowercase, but not both).

type of record

A data element in the leader that with bibliographic level, specifies the characteristics and defines the components of the record.

variable control field

See control field

variable data field

See data field

variable field

A field whose length is determined for each occurrence by the length of data comprising that occurrence.  There are two types of variable fields - control fields and data fields.

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Record Structure