|in addition to
storing info about a physical item, a MARC record can either link that same
description for a digital copy of it (see the records in the catalog for
anything in VARIATIONS), or they could describe only a digital item. There's
a standing debate out there about how to deal with an item held both analog
and digital, whether to have one record describing the physical item but
having a URL for the digitized version, or having two separate records.