  Various XML-based approaches aimed at representing compound digital assets
have emerged over the last several years. Approaches that are of specific
relevance to the digital library community include the Metadata Encoding and
Transmission Standard (METS), the IMS Content Packaging XML Binding, and the
XML Formatted Data Units (XFDU) developed by CCSDS Panel 2. The MPEG-21 Digital
Item Declaration (MPEG-21 DID) is another standard specifying the
representation of digital assets in XML that, so far, has received little
attention in the digital library community. This article gives a brief insight
into the MPEG-21 standardization effort, highlights the major characteristics
of the MPEG-21 DID Abstract Model, and describes the MPEG-21 Digital Item
Declaration Language (MPEG-21 DIDL), an XML syntax for the representation of
digital assets based on the MPEG-21 DID Abstract Model. Also, it briefly
demonstrates the potential relevance of MPEG-21 DID to the digital library
community by describing its use in the aDORe repository environment at the
Research Library of the Los Alamos National Laboratory (LANL) for the
representation of digital assets.
