Appendix A contains descriptions of subfields that are used to link field data to other fields.  These subfields are defined for most fields in the format, thus their descriptions are brought together in this appendix.  The subfields are included in field level subfield lists wherever they are defined, with links to this appendix.

Specific subfield information:

$0  Authority record control number or standard number

$1  Real World Object URI

$6  Linkage

$8  Field link and sequence number

Content designator history:

$0 - Authority record control number  [new, 2007]

$0 - Authority record control number  [redefined, 2010]

$0 - Authority record control number or standard number  [redescribed, 2016]

In 2016, the requirement to precede a dereferenceable URI (such as an HTTP URI) in subfield $0 with the parenthetical prefix code "(uri)" was removed.

$1 - Real World Object URI  [new, 2017]

$6 - Linkage [redescribed, 2018]

Scope of $6 broadened to allow for the recording of script identification codes taken from ISO 15924.

$8 - Field link and sequence number

p - Metadata provenance  [new, 2012]

u - General linking, type unspecified  [new, 2016]

See also:

Appendices