648 Subject Added Entry - Chronological Term

Field definition and scope:

Field 648 contains a chronological term used as a subject added entry.

Subject added entries are assigned to a community information record to provide access according to generally accepted thesaurus-building rules (e.g., Library of Congress Subject Headings (LCSH), Medical Subject Headings (MeSH), Faceted Application of Subject Terminology (FAST)). Field 648 may be used by any institution assigning subject headings based on the lists and authority files identified in the second indicator position or in subfield $2 (Source of heading or term).

Field 648 is repeatable.

Guidelines for applying content designators:

The content designators identify the subelements occurring in chronological terms and subdivisions.

For indicator and subfield code definitions and examples, and designator repeatability, see table below:

Position	Description	Repeatability
Field 648	Subject Added Entry - Chronological Term	R
Indicator:
First	Undefined; contains a blank

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

Subfield code:
$a	Chronological term	NR
$v	Form subdivision	R
$x	General subdivision	R
$y	Chronological subdivision	R
$z	Geographic subdivision	R
$0	Authority record control number or standard number	R
$1	Real World Object URI	R
$2	Source of heading or term	NR
$3	Materials specified	NR
$6	Linkage	NR
$8	Field link and sequence number	R

Input conventions:

Display constant

Content designator history:

Subfield $0 - Authority record control number [new, 2007]

Subfield $0 - Authority record control number [redefined, 2010]

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