Subfield $0 contains the system control number of the related authority or classification record, or a standard identifier such as an International Standard Name Identifier (ISNI).  These identifiers may be in the form of text or a URI.  If the identifier is text, the control number or identifier is preceded by the appropriate MARC Organization code (for a related authority record) or the Standard Identifier source code (for a standard identifier scheme), enclosed in parentheses.  When the identifier is given in the form of a Web retrieval protocol, e.g., HTTP URI, no preceding parenthetical is used.

See MARC Code List for Organizations for a listing of organization codes and Standard Identifier Source Codes for code systems for standard identifiers.  Subfield $0 is repeatable for different control numbers or identifiers.

Note:  Subfield $0 may be referred to in the field descriptions as Authority record control number.

Examples:

100  1#  $aBach, Johann Sebastian.$4aut$0(DE-101c)310008891

100  1#  $aTrollope, Anthony,$d1815-1882.$0(isni)1234567899999799

710  2#  $aCalifornia Poets in the Schools (Project),$eissuing body,$epublisher.$0http://id.loc.gov/authorities/names/n85319780

See also:

Appendix A:  Control Subfields