Notes on METS

METS, the Metadata Encoding Transmission Standard, was developed by the Digital Library Federation and is housed at the Library of Congress.

What it is: "Maintaining a library of digital objects of necessity requires maintaining metadata about those objects.[....] Without structural metadata, the page image or text files comprising the digital work are of little use, and without technical metadata regarding the digitization process, scholars may be unsure of how accurate a reflection of the original the digital version provides. For internal management purposes, a library must have access to appropriate technical metadata in order to periodically refresh and migrate the data, ensuring the durability of valuable resources." (From the METS Overview)

METS was developed based on work by the Library of Congress on its Making of America II.

A typical METS document consists of four components (excerpted from the METS Overview at the Library of Congress website):

  1. Descriptive Metadata [e.g. cataloging information, describing what the materials are about]
  2. Administrative Metadata - The administrative metadata section provides information regarding how the files were created and stored, intellectual property rights, metadata regarding the original source object from which the digital library object derives, and information regarding the provenance of the files comprising the digital library object (i.e., master/derivative file relationships, and migration/transformation information).
  3. File Groups - The file group section lists all files comprising all electronic versions of the digital object.
  4. Structural Map - The structural map is the heart of a METS document. It outlines a hierarchical structure for the digital library object, and links the elements of that structure to content files and metadata that pertain to each element.

METS is an extremely generic xml schema coming out of the library world, but it's much less geared towards a specific type of community practice or type of content than the EAD. A METS document encodes one single Digital Object, which may comprise many multimedia files (image, audio, video). The object typically contains a hierarchical structure (such as the chapter / page structure of a book) pointing toward the surrogates. METS objects may also carry extensive descriptive metadata about the original (often physical) object described, used for discovery; as well as extensive administrative metadata such as technical metadata about the multimedia files, or rights metadata etc. It looks like METS will find wide adoption as a file exchange format, as a means to manage archival digital files and as a way to present digital surrogates.

Guenter Waibel of the Berkeley Art Museum & Pacific Film Archive wrote on the EAD list, 24 Apr 2002, comparing EAD and METS:

METS is an extremely generic xml schema coming out of the library world, but it's much less geared towards a specific type of community practice or type of content than the EAD. A METS document encodes one single Digital Object, which may comprise many multimedia files (image, audio, video). The object typically contains a hierarchical structure (such as the chapter / page structure of a book) pointing toward the surrogates. METS objects may also carry extensive descriptive metadata about the original (often physical) object described, used for discovery; as well as extensive administrative metadata such as technical metadata about the multimedia files, or rights metadata etc. It looks like METS will find wide adoption as a file exchange format, as a means to manage archival digital files and as a way to present digital surrogates.

While the EAD will be used to describe and structure collections, METS may be used to deliver extremely granular digital surrogates of the objects in the collections. The Online Archive of California (OAC) has adopted a strategy to use METS that way, and we've just started developing a best practise guide for METS as implemented in the OAC.

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