Subfield code $1 - Real World Object URI  (Appendix A:  Control Subfields)

Subfield $1 contains a URI that identifies a description of an entity, sometimes referred to as a Thing, a Real World Object or RWO, whether actual or conceptual.  When dereferenced, the URI points to a description of that entity.  A URI that identifies a name or label for an entity is contained in $0.

Examples:

100  1#  $aObama, Michelle,$d1964-$0http://id.loc.gov/authorities/names/n2008054754$1http://viaf.org/viaf/81404344

100  1#  $aSanta Claus$0http://id.loc.gov/authorities/names/no2015039717$1http://dbpedia.org/resource/Santa_Claus

700  1#  $aJemison, Mae,$d1965-$0http://id.loc.gov/authorities/names/n95004729$1http://id.loc.gov/rwo/agents/n95004729

See also:

Appendix A:  Control Subfields