An rlgid is a unique identifier assigned to any bibliographic record
either within the RLG Union Catalog or any RLG-mounted database. These
identifiers are assigned automatically on records entered online and
maintained on batch-loaded records so as to assure uniqueness in records
loaded in batch form. rlgid identifiers are composed of digits, letters,
and (optionally) a single dash. There is no explicit limit on the length
of an rlgid, and an rlgid does not carry significance other than to
identify a specific bibliographic record.

The uri provided below describes rlgid structure within the RLG Union
Catalog; equivalent structures (with different letter identifiers) are
used for other RLG-mounted databases.

RLG identifiers (rlgid instances) in the RLG Union Catalog frequently
appear in the 035 tag (System Control Number) of MARC21 records. In
these cases, the rlgid is preceded by a code contained within parentheses
and representing the originating institution, e.g. (CStRLIN). The leading
code, including parentheses and any following spaces, is stripped off to
create a proper rlgid.

Letters within rlgid instances are not case-sensitive.

The single dash that may appear within an rlg may be omitted (but not
replaced by a space).