X48 Chronological Terms - General Information

Field definition and scope:

Each chronological term field is unique in its definition and scope. For specific information, select from the list below.

148 Heading - Chronological Term (NR)

448 See From Tracing - Chronological Term (R)

748 Established Heading Linking Entry - Chronological Term (R)

Record requirements: The National level record requirement for the chronological term fields is Mandatory if applicable, except for field 748 which is Optional. For the national level requirements by subfield, see the specific field.

Field repeatability: See the specific field for its repeatability.

Guidelines for applying content designators:

The content designators identify the subelements occurring in chronological term headings constructed according to generally accepted thesaurus-building conventions (e.g., Faceted Application of Subject Terminology (FAST)).

Chronological terms include dates that are used as the lead element of subject or added entry access fields in bibliographic records.

A chronological term that is authorized for use only as a subject subdivision part of an extended subject heading is contained in a 182 (Chronological Subdivision) field.

The indicators, subfield codes, and input conventions for the chronological term fields 148, 448, 548, and 748 follow similar patterns. Guidelines for applying them are below. Subfields are grouped by type of entry.

For indicator and subfield code definitions and examples, National level (NLR) record requirements, and designator repeatability, see table below. An asterisk ( * ) in the column indicates that the requirement varies. See table in the specific field.:

Position	Description	NLR	Repeatability
Field X48	Chronological Terms	*	*
Indicator:
First	Undefined; contains a blank	M

Second
148, 448, 548	Undefined; contains a blank	M

748	Thesaurus	M
0	Library of Congress Subject Headings/Name authority file	A
1	LC subject headings for children's literature	A
2	Medical Subject Headings/NLM name authority file	A
3	National Agricultural Library subject authority file	A
4	Source not specified	A
5	Canadian Subject Headings/LAC name authority file	A
6	Répertoire de vedettes-matière	A
7	Source specified in subfield $2	A

Subfield code:
	Main term portion
$a	Chronological term	M	NR

	Subject subdivision portion
$v	Form subdivision	A	R
$x	General subdivision	A	R
$y	Chronological subdivision	A	R
$z	Geographic subdivision	A	R

	Tracing and linking subfields
$i	Relationship information [448, 548, 748]	current - A earlier - A	R
$w	Control subfield [448, 548, 748]	A	NR
$0	Authority record control number or standard number [548, 748]	A	R
$1	Real World Object URI [548, 748]		R
$2	Source of heading or term [748]	A	NR
$4	Relationship [448, 548, 748]	O	R
$5	Institution to which field applies [448, 548, 748]	A	R
$6	Linkage	A	NR
$8	Field link and sequence number	O	R

Input conventions:

Punctuation

Spacing

Display constant for X48 fields

Content designator history:

Subfield $i - Reference instruction phrase [448, 548] [redefined, 2009]

Subfield $i - Relationship information [748] [new, 2014]

Subfield $0 - Record control number [548, 748] [redefined, 2010]

Subfield $1 - Real World Object URI [548, 748] [new, 2017]

Subfield $4 - Relationship code [448, 548] [new, 2009]

Subfield $4 - Relationship code [748] [new, 2014]

Subfield $4 - Relationship code [448, 548, 748] [renamed, 2017] [redescribed, 2017]: Subfield $4 was renamed to Relationship and redescribed to allow for the recording of relationship URIs in addition to MARC and non-MARC codes.