7XX Heading Linking Entries - General Information

Definition and scope:

The 7XX Heading Linking Entry fields provide a machine link within a system between equivalent or hierarchical headings whether they are structured in the same or different form, are from the same or different authority files or printed thesauri, or whether they exist as separate authority records. The inclusion of a linking entry field in an established heading or established heading and subdivision record for a name, name/title, uniform title, topical term, form term, or extended subject heading or in an established heading record for an authorized subject subdivision may be used to relate such headings as:

equivalent names in a multilingual thesaurus

Example: Library and Archives Canada English heading Francis, of Assisi, Saint, 1182-1226 and Library and Archives Canada French heading François, d'Assise, saint, 1182-1226

names from different thesauri representing hierarchical (i.e., broader or narrower) relationships, or associative relationships

equivalent topical term headings in different authority systems

Example: Library of Congress Subject Headings (LCSH) headings Medical referral and Medical consultation and Medical Subject Headings (MeSH) heading Referral and Consultation

a topical term heading (field 150) and the same or similar term used as a subject subdivision (field 78X)

Example: established term History and the subject subdivision History

Example: established term Twentieth century and the subject subdivision 20th century

a geographic name heading (field 151) and the indirect form of that name used as a geographic subject subdivision (field 781)

Example: established heading Rome (N.Y.) and the subject subdivision New York (State)--Rome.

a genre/form term heading (field 155) and the same or similar term used as a form subject subdivision (field 785)

Example: established heading Periodicals and the subject subdivision Periodicals.

The 7XX field tag identifies whether the heading linking entry field contains an established heading (fields 700-762) or an authorized subdivision heading (fields 780-785). The second indicator or subfield $2 identify the authority system to which the heading in field 7XX belongs. Subfield $0 (Authority record control number or standard number) contains the system control number or standard number of the related record when a separate MARC authority record exists for the 7XX heading.

A relationship that cannot be adequately expressed by the 700-785 linking entry fields is described textually in field 788.

Guidelines for applying content designators:

Guidelines for the second indicator position (Thesaurus), subfield $2 (Source of heading or term), subfield $w (Control subfield), subfield $i (Relationship information), and subfield $4 (Relationship) in the 7XX fields, as well as special instructions for field 788 are provided below. All other content designators in the 7XX fields are defined in the specific fields and in the X00-X85 General Information sections for each corresponding field.

First indicator position and all of the subfield codes defined for field 788 (Complex Linking Entry Data) are described in the description of that field. The second indicator position is described in this section.

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 7XX	Heading Linking Entries	O	*
Indicator:
First	First indicator position	M

Second	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:
$i	Relationship information	A	R
$w/	Control subfield	A	NR
	/0 Link display	M
	/0-a Link not displayed
	/0-b Link not displayed, field 788 used
	/0-c Link not displayed, non-7XX field used
	/0-n Not applicable
	/1 Replacement complexity	A
	/1-a Heading replacement does not require review
	/1-b Heading replacement requires review
	/1-n Not applicable
$2	Source of heading or term	A	NR
$4	Relationship	O	R

Input conventions:

The general input conventions for the 7XX fields are provided in the specific fields and in the X00-X85 General Information sections for each type of heading.

Order of subfields

Relationship codes

Display constants for 7XX Linking Entries

Content designator history:

747 Established Heading Linking Entry - Named Event [new, 2016]

748 - Established Heading Linking Entry - Chronological Term [new, 2002]

762 - Established Heading Linking Entry - Medium of Performance Term [new, 2013]

9XX - Equivalent Headings [obsolete, 1997] [CAN/MARC only]: The 9XX heading fields were made obsolete in 1997 since the USMARC 7XX fields were already defined for equivalent headings.

Subfield $i - Relationship information [new, 2014]

Subfields $u - Record control number [obsolete, 1997] [USMARC only]

$0 - Record control number [new, 1997]

$v - Form subdivision [redefined, 1995] [USMARC only]

From 1993 to 1995, subfield $v was defined as Record control number in the 7XX Heading Linking Entry fields. In 1995, subfield $v was redefined as Form subdivision and subfield $u was defined as Record control number. In 1997, subfield $0 was defined as Record control number and $u was made obsolete.

Subfield $w/1 - Replacement complexity [new, 2002]: In 2002, subfield $w/1 was defined with the following codes: a (Heading replacement does not require review); b (Heading replacement requires review); and n (Not applicable).

Subfield $4 - Relationship code [new, 2014]

Subfield $4 - Relationship code [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.

DCM Z1 Instructions:

7XX Heading Linking Entries