Page 148 - Building Digital Libraries

Metadata Formats

existed—MARC21XML and Dublin Core. Each of these two formats would
prove to be undesirable for several reasons: Dublin Core due to its inability
to capture metadata at a fine enough level of granularity, and MARC21XML
due to its reliance on MARC structures and rules. This caused the Library of
Congress to develop MODS, a simpler subset of MARC that could produce
rich descriptions at the desired level of granularity. However, lost in this
development was the release of a complementary technology, METS. While
MODS provided a robust format for bibliographic metadata description, a
method still needed to be developed that would bind together the adminis-
trative, structural, and bibliographic metadata of a digital object. Moreover,
loading and exporting digital objects from a digital repository would need
to include this information as well—meaning that the digital object must be
able to retain its metadata, in all its forms, to be useful outside of the host
system. So, in essence, METS was created to be this glue for digital objects,
binding together all relevant metadata relating to item structure, descrip-
tion, and administration.
The Library of Congress started experimenting with the mixing of
METS and MODS almost immediately after releasing the specifications in
2002. Later that year, the Library of Congress started work on the Digital
Audio-Visual Preservation Prototyping project, which combined the use of
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MODS as the bibliographic description framework with METS as the digital
object framework. Since then, the Library of Congress has produced a wide
variety of projects utilizing the MODS/METS combination.

METS at a Glance
Before looking at how METS is being used within current digital repository
efforts, we need to quickly take a look at what makes up a METS document.
Obviously, this is by no means comprehensive, since the current METS
documentation spans hundreds of pages and examples, but it should pro-
vide an adequate overview of what makes up a METS document, and how
those elements tie the various pieces of a digital object together. There are
currently seven sections to a METS document. These sections are:
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ELEMENT DESCRIPTION
metsHdr METS Header: tag group stores information about the METS document
itself, not the digital object which it describes.
dmdSec Descriptive Metadata Section: tag group stores all the descriptive
metadata for all items referenced by the METS document.
amdSec Administrative Metadata Section: tag group stores all the administrative
metadata for all items referenced by the METS document.
fileSec Content File Section: tag group stores information on all files referenced
by the METS document.
structMap Structural Map: tag group stores the hierarchical arrangement of items
referenced by the digital object.
structLink Structural Map Linking: tag group stores linking information between
referenced items in the structural map section.
behaviorSec Behavior Section: tag group defines behaviors associated with the
referenced items in a METS document (i.e., executable behaviors, etc.).
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