New metadata standards for digital resources: MODS and METS

Bulletin of the American Society for Information Science & Technology, Dec 2002/Jan 2003 by Guenther, Rebecca, McCallum, Sally

The METS "Package"

The six parts of the METS package or document are as follows: header, descriptive metadata, administrative metadata, file section, structural map and behavior section. They are all optional except for the header and structural map, which are needed for basic access to the digital resource. The descriptive, administrative and behavior sections may reside in the METS document or be external. If they are internal, XML schemas are preferred. If the metadata for these sections is external and merely pointed to from the appropriate section of the METS document, the metadata may be of any type and format. For descriptive metadata it may even be an entry in a catalog if the catalog record can be adequately referenced.

The METS descriptive metadata section is the most familiar to librarians, as it contains cataloging and finding-aid data. There are several established schemas that can be used for the descriptive metadata - including MODS, which was designed with a special focus on electronic resources; Dublin Core, when only minimal data is needed; or MARCXML when full MARC record information is available.

The administrative metadata is the most critical for use and preservation of the digital resource. Here resides source information such as resource creation date, resource format information, resource use information, digital provenance and copyright and license information. This section may contain information on past transformations and migrations of the data and master/derivative information, all useful for preservation purposes. XML schemas are not yet standard for most of this information but the METS project is pushing their development. For example, the recently completed NISO data dictionary for technical metadata for still images (www.niso.org/standards/resources/Z39 87_trial-use.pdf) is being used through a supporting XML schema, MIX (Metadata Imagining in XML) (www.loc.gov/mix/). Project participants also have drafts prepared for the technical data for text, audio and moving images. The draft schemas are available from the METS website.

The behavior section of the METS document contains pointers to computer programs or applications that are used to display digital objects such as page-turners or audio players. The behavior information is intended to assist in providing "disseminators" for end user access.

The header, file group and structural map sections may only reside in the METS document - there is no option to point to them outside. The file section identifies all the files the object clusters, such as thumbnails, master archival, pdf versions and text-encoded versions. The structural map contains a clear layout of the hierarchical structure of the document. An important feature of METS is that the structural map may point to parts of the descriptive and administrative metadata from different places on the structure hierarchy of the resource, enabling linking to subparts of digital resources, such as cuts on sound recordings. The header also gives information about the METS document itself, such as identifiers, date created, dates updated and status.