Metadata Reference Guide

About the Metadata Encoding and Transmission Standard (METS)

Documentation:
From the METS home page <http://www.loc.gov/standards/mets/>: "The METS schema is a standard for encoding descriptive, administrative, and structural metadata regarding objects within a digital library, expressed using the XML schema language of the World Wide Web Consortium."

Constituency:
Again, from the METS site: "The standard is maintained in the Network Development and MARC Standards Office of the Library of Congress, and is being developed as an initiative of the Digital Library Federation.

Its initial users include several large governmental (e.g. LoC) and ARL libraries (UCBerkeley, Harvard, NYU, MIT, etc.). These users and their projects using METS are typically concerned with creation, maintenance, transmission, and preservation of large digital collections over both the short and long term. METS is providing a standard way to describe the logical structure of objects found in digital collections, and to bind a wide range of descriptive and other metadata types to those structural descriptions.

History of use:
METS grew out of the Making of America II (MOA2) <http://sunsite.berkeley.edu/MOA2/> project's MOA DTD. Its utility in that project, combined with growing interest in the broader community for a standard accomplishing these goals, led to a broader project to define the standard.

Early prototypes of METS implementations were tested by MOA participants and peer libraries, and ongoing development is led by individuals and staff from many of these same projects and institutions, plus a broader range of parties.

Draft versions of the METS schema have been released every few months since fall 2001. The current version of METS is "1.0 zeta"; a new version is current proposed as "1.1".

Prerequisites:
METS is defined as an XML Schema, requiring staff and software support capable of operating on datasets using standard XML Schema knowledge and tools.

Because of its flexibility and potential specificity, METS also requires a certain minimum of descriptive and technical expertise; while it may be applied in simple applications, as can simpler standards like the Dublin Core, its power is best utilized in projects of greater scale and complexity than that required by Dublin Core implementations. Note that this is, of course, by definition, not by any failing of either standard or community.

Content:
METS documents require a "Structural Map" of objects, and optionally may also include descriptive, administrative, file grouping, or behavioral metadata which further describe a bundle of objects collectively or any part of the bundle's objects' structure, by reference objects identified within the Structural Map.

A METS document may contain, in any of these metadata sections, wrapped or explicitly encoded metadata bundles, or it may reference metadata external to the objects in hand.
Similarly, a METS document may contain, wrapped or explicitly encoded within the METS document itself, the objects the METS document is describing. It may also reference its described objects as a document distinct from these objects.

Encoding:
Because METS is an XML Schema definition, encoding of METS documents adhere to XML and XML Schema encoding requirements. Where the METS schema provides for wrapping of metadata or content objects within a METS document instance, those provisions also follow XML and XML Schema encoding standards.

Important related efforts:
Work is ongoing among the METS community to develop registries of best practice guides and implementations. Also, work to standardize commonly used "extension schema" (e.g., how to encode Dublin Core metadata within METS) is ongoing as well. Communication these efforts seem to transpire publicly on the METS listserv (hosted by the LoC, subscription details for which are available at the METS site).

The OAIS <http://ssdoo.gsfc.nasa.gov/nost/isoas/> Reference Model defines Submission, Archival, and Dissemination Information Packages as core components of digital archival systems. Many library community members are interested in using METS in their local systems' definitions of SIP, AIP, and DIP object types (including DSpace).

Example implementations:
Several example documents are provided from UCBerkeley and Harvard library on the METS web site.

A free-as-in-speech METS java toolkit has been publicly released by staff at Harvard:
http://hul.harvard.edu/mets/

The DSpace project is intended to use METS as its logical object descriptive encoding scheme.