Subfield $0 contains the system control number of the related authority record, or a standard identifier such as an International Standard Name Identifier (ISNI).  These identifiers may be in the form of text or a Uniform Resource Identifier (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.

Subfield $0 may contain a URI that identifies a name or label for an entity.  When dereferenced, the URI points to information describing that name.  A URI that directly identifies the entity itself is contained in subfield $1.

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.

To return:

Use the key.

See also:

Appendix A:  Control Subfields