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DATE: December 20, 2013

NAME: Relationships Between Subject Headings from Different Thesauri in the MARC 21 Authority Format

SOURCE: German National Library

SUMMARY: This paper discusses a way to designate relationships between entries of different thesauri in a MARC authority record.


RELATED: Relationship designators (AD); Thesauri (AD); Heading linking entry fields (AD); Subfield $i, in 7XX fields (AD); Relationship information (AD); Subfield $4, in 7XX fields; (AD); Relationship code (AD)

12/20/13 – Made available to the MARC community for discussion.

01/26/14 – Results of MARC Advisory Committee discussion: The Committee was in favor of defining subfields $i and $4 in the 7XX throughout the Authority format to enable the process of relating headings from different thesauri in both human readable and coded forms.  The option of adding a third position to 7XX $w was not preferred.  DNB will submit a proposal at Annual 2014. 

Discussion Paper No. 2014-DP02: Relationships Between Subject Headings from Different Thesauri


Mapping subject headings from different thesauri

In Germany there is a tradition of mapping different thesauri.  In the project MACS ("Multilingual Access to Subjects") as well as in the so called "Crosskonkordanzen" a detailed mapping from subject headings of the Schlagwort-Normdatei (SWD, Authority File for Subject Headings) to several other thesauri is done.

End users can benefit from these mapping results when they start searching and navigating based on a known thesaurus, and are guided by relationships to other thesauri, visibly or in the background.

Currently, the results of these intellectual efforts are kept in separated records.  With the integration of the SWD into the "Gemeinsame Normdatei" (GND, Integrated Authority File) there is a need to develop a format solution. Because the exchange format for the GND is MARC Authority, and because the cataloging format of the GND is based on MARC Authority, we have to find a solution in the MARC Authority format.

The mappings are using the framework given by ISO 25964 "Information and documentation - Thesauri and interoperability with other vocabularies", part 2 "Interoperability with other vocabularies" (ISO 25964-2).

Many of the detailed mappings are of the type "simple equivalence" ("EQ"). In other cases, there is a hierarchical relationship between one subject heading from thesaurus A to a second subject heading from thesaurus B, either of the type "broader mapping" ("BM") or "narrower mapping" ("NM"). In addition, there are cases where the relationship is an associative one, called a "related mapping" "(RM").

Combined with this distinction, there is a majority of cases where there is a one-to-one-relationship. However there are as well one-to-many-relationships (one-to-two, one-to-three), and, vice versa, a few many-to-one-relationships (two-to-one, three-to-one).


MARC Authority 7XX

In the MARC Authority format, the 7XX fields contain the "Heading Linking Entries".  According to the documentation at,

"The 7XX Heading Linking Entry fields provide a machine link within a system between equivalent 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."

In our context of mappings between thesauri, we intend to use the 7XX fields to "provide a machine link within a system between equivalent headings [...] from [...] different authority files". The fields contain a subfield $0, so linking via an "Authority record control number or standard number" is feasible. The fields contain a subfield $2, so that the "Source of heading or term" can be expressed, as listed under the "Subject Heading and Term Source Codes". And the fields contain a subfield $8 "Field link and sequence number", so that grouping different fields in the same record and sequencing them is possible.

What is missing in the 7XX fields is the designation of a relationship beyond a "simple equivalence". In cases of hierarchical ("broader" or "narrower") or associative relationships, fields 7XX lack a way of expressing the type of relationship.

We analyzed 7XX subfield $w "Control subfield", with its two positions "/0 - Link display" and "/1 - Replacement complexity". In contrast, subfield $w "Control subfield" from fields 4XX and 5XX of the MARC Authority format has a position /0 which is defined as "Special relationship", with the possible values:

a - Earlier heading
b - Later heading
d - Acronym
f - Musical composition
g - Broader term
h - Narrower term
i - Reference instruction phrase in subfield $i
n - Not applicable
r - Relationship designation in $i or $4
t - Immediate parent body

There is one field in the 7XX range, field 788 "Complex Linking Entry Data", where relationships can be described "when the linking relationship between headings from different subject heading systems or thesauri cannot be adequately conveyed by fields 700-785". Field 788 is the only one of the 7XX range where a subfield $i "Explanatory text" is defined. We don't intend to use 788, as it can transport textual information, and it doesn't tell by its tag which kind of entity it links to.

We analyzed the 4XX and 5XX fields of the MARC Authority format, which contain subfields $i "Relationship information" (R) and $4 "Relationship code" (R). Our thinking is now headed in the direction of having subfields $i "Relationship information" (R) and $4 "Relationship code" (R) defined in the 7XX fields as well.

The content of subfield $i is textual, controlled by cataloging rules or other policy regulations. The content of subfield $4 is based on the same rules, but controlled by a closed list of codes, maintained by LC's NDMSO, and documented in the MARC Code List for Relators.

Summing up, the approach taken by this discussion paper is to define two new subfields for fields 7XX:

$i - Relationship information (R)


$4 - Relationship code (R)


Notes on the examples:

The examples are real-life ones, taken from existing mapping records. They are describing German language topical terms and their mappings.

The new subfields $i and $4 and their contents are underlined.

The content of subfields $4 are the tag values in ISO 25964-2. Here, they are used as purely illustrative, and not meant to anticipate any future decisions.

"EQ" - Equivalence
"BM" - Broader mapping
"NM" - Narrower mapping
"RM" - Related mapping

"stw" in $2:
Standard-Thesaurus Wirtschaft = STW Thesaurus for Economics  (Kiel: ZBW - Deutsche Zentralbibliothek fur Wirtschaftswissenschaften)

"thesoz" in $2:
Thesaurus for the Social Sciences (Germany: GESIS - Leibniz Institute for the Social Sciences)

Example 1: Simple equivalence

LDR xxxxxnz#a22yyyyyn#4500
001 966658655
003 DE-101
035 ## $a (DE-588)4145068-1
150 ## $a Betriebsstörung
750 #7 $0 ([ISIL STW])19247-6 $a Betriebliche Störung $4 EQ $2 stw

Example 2: Broader term

LDR xxxxxnz#a22yyyyyn#4500
001 970531885
003 DE-101
035 ## $a (DE-588) 4142176-0
150 ## $a Ambulante Behandlung
750 #7 $i Oberbegriff $a Ambulante Versorgung $4 BM $2 thesoz

Example 3: Narrower term

LDR xxxxxnz#a22yyyyyn#4500
001 966660064
003 DE-101
035 ## $a (DE-588) 4631982-7
150 ## $a Energieversorgungsnetz
750 #7 $0 ([ISIL STW])18361-6 $i Unterbegriff $a Stromnetz $4 NM $2 stw

Example 4: Associative relationship

LDR xxxxxnz#a22yyyyyn#4500
001 970532083
003 DE-101
035 ## $a (DE-588) 04225753-0
150 ## $a Bezugsquelle
750 #7 $i Verwandter Begriff $a Anbieter $4< RM $2 thesoz

Example 5: Simple equivalence, 1-to-2

5.1. Without $8's:

LDR xxxxxnz#a22yyyyyn#4500
001 966661230
003 DE-101
035 ## $a (DE-588) 4139099-4
150 ## $a Gastarif
750 #7 $0 ([ISIL STW])14603-0 $a Gas $4 EQ $2 stw
750 #7 $0 ([ISIL STW])10213-5 $a Preis $4 EQ $2 stw

5.2. Using $8's:

LDR xxxxxnz#a22yyyyyn#4500
001 966661230
003 DE-101
035 ## $a (DE-588) 4139099-4
150 ## $a Gastarif
750 #7 $8 1 $0 ([ISIL STW])14603-0 $a Gas $4 EQ $2 stw
750 #7 $8 1 $0 ([ISIL STW])10213-5 $a Preis $4 EQ $2 stw

Example 6: Broader term, 1-to-2

LDR xxxxxnz#a22yyyyyn#4500
001 966663691
003 DE-101
035 ## $a (DE-588) 4627895-3
150 ## $a Kleinunternehmerin
750 #7 $0 ([ISIL STW])13992-3 $i Oberbegriff $a Unternehmer $4 BM $2 stw
750 #7 $0 ([ISIL STW])15920-4 $i Oberbegriff $a Frauen $4 BM $2 stw

Example 7: Narrower term, 1-to-2

LDR xxxxxnz#a22yyyyyn#4500
001 971391130
003 DE-101
035 ## $a (DE-588) 4120950-3
150 ## $a Ausbildungsnachweis
750 #7 $i Unterbegriff $a Ausbildung $4 NM $2 thesoz
750 #7 $i Unterbegriff $a Zeugnis $4 NM $2 thesoz


(There is no example for a 2-to-1 relationship: This would result in a record with two 1XX fields, or with two fields 260, and no 1XX field at all.)


BIBFRAME currently has the capability to express these relationships to external thesauri in MADSRDF <> with the following properties:  hasExactExternalAuthority, hasBroaderExternalAuthority, hasNarrowerExternalAuthority, hasCloseExternalAuthority, hasReciprocalExternalAuthority.  Depending on the definition of "related mapping" (close?), the relationships appear to be covered.


5.1. Does it make sense to include relationships between single subject headings from different thesauri into one of the thesauri used (i.e. into the GND)?

5.2. Is the direction of defining $i and $4 in MARC Authority fields 7XX for the designation of inter-thesauri mappings a feasible one?

5.3. What should be the solution for a 2-to-1 relationship in MARC Authority?

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