6XX fields contain subject access entries and terms. Most of these fields contain subject added entries or access terms based on the lists and authority files identified in the second indicator (Subject heading system/thesaurus) or in subfield $2 (Source of subject heading or term). One field contains uncontrolled subject access data.
For mixed materials and collections under archival control, considerable use is made of the 6XX fields to reflect the subject content of the described materials through controlled and uncontrolled headings and terms. The 7XX fields are used less frequently to provide access.
Descriptions of the first indicator and all subfield codes, as well as input conventions for the 600, 610, 611, and 630 fields, are given in the following General Information sections: X00, X10, X11 and X30. The second indicator is described in the specific section for each field. All content designators for the 650-658 fields are described in the specific section for each field.
Field 600-651 - Subject added entries
Indicator 2 - Subject heading system/thesaurus
In 1982 the use of the second indicator value in subject added entry fields 600-651 was expanded from specifying the organization that assigned the subject added entry to specifying the subject heading system, thesaurus, or authority file used by an organization to assign the subject added entry. Accordingly, values 0-3 and 5-6 became authoritative-agency data elements and their definitions were changed to the names of the list or authority file. The definition of value 4 was changed from Other subject heading. Prior to 1975, value 5 was defined in the visual materials specifications as Subject heading to be printed only in LC book catalog. Prior to 1977, value 5 was defined in the archival and manuscripts control specifications as National Union Catalog of Manuscripts (NUCMC) subject heading.
Field 648 - Subject Added Entry-Chronological Term [NEW, 2002]
Field 652 - Subject Added Entry-Reversed Geographic [OBSOLETE, 1980]
Field 652 was an agency-defined field used by the Library of Congress for reversed geographic added entries assigned to materials classed in LC classification number span G1000-G9999. For each regular Topic-Place subject heading assigned, a reversed Place--Topic heading was also assigned. Both indicator positions were undefined. The subfield codes were: $a (Geographic name or place element), $x (General subject subdivision), $y (Chronological subject subdivision), $z (Geographic subject subdivision).
Field 662 - Subject Added Entry - Hierarchical Place Name [NEW, 2005]
Field 680 - PRECIS Descriptor String [OBSOLETE, 1991] [CAN/MARC only]
PRECIS Descriptor String is a sequence of subject index terms in which each term is preceded by a code which determines how it should appear in entries generated by a computer. The first indicator was undefined. The second indicator values 0-9 were used to link alternative subject statements to the corresponding Dewey classification number. Subfields $a-$z contained the text of the PRECIS Descriptor String.
Field 681 - PRECIS Subject Indicator Number (SIN) [OBSOLETE, 1991] [CAN/MARC only]
PRECIS Subject Indicator Number (SIN) is a fixed-length number ending in a modulus 11 check digit. It identifies uniquely the address of the PRECIS data consisting of string and Reference Indicator Number (RIN). The first indicator was undefined. The second indicator values 0-9 were used to link the indicator to the corresponding PRECIS string and other associated subject data. Only subfield $a (PRECIS subject indicator number (SIN)) was defined.
Field 683 - PRECIS Reference Indicator Number (RIN) [OBSOLETE, 1991] [CAN/MARC only]
PRECIS Reference Indicator Number (RIN) is a fixed-length number ending in a modulus 11 check digit which identifies the address of a term in the machine-held thesaurus used as the source of 'See' and 'See also' references in a printed index. The first indicator was undefined. The second indicator values 0-9 were used to link the index numbers to the corresponding PRECIS descriptor string. Only subfield $a (Reference indicator number (RIN)) was defined.