Digital Preservation ― Preservation Metadata and METS

Preservation metadata is information that supports and documents activities related to digital preservation.  It is information that is used in supporting the processes of ensuring the core preservation processes of availability, identity, understandability, authenticity, viability and renderability.  While some of these activities require descriptive and structural metadata, the majority of it is administrative metadata. The preservation of digital objects requires extensive documentation that accumulates over the life of the digital object.  Management of this metadata is handled through the PREservation Metadata Implementation Strategies (PREMIS), a set of core preservation metadata likely to be needed to be used to manage digital resources in a digital repository.  Due to the limited implementation of PREMIS, Priscilla Caplan, Chair of the PREMIS working group, notes, “…nobody knows whether it works.  That is, there has not been enough experience applying preservation strategies to know whether today’s preservation metadata schemes actually support the process of long term preservation.”

OAIS requires packaging information to describe the various types of OAIS information—ingest dissemination, etc.  Within the cultural heritage community, Metadata Encoding and Transmission Standard (METS), is the mostly commonly used standard. An XML-based schema, METS is designed to be an overall framework in which all metadata associated with a digital object can be stored.  The following describes the components of METS.

• Descriptive Metadata - The descriptive metadata section may point to descriptive metadata external to the METS document (e.g., a MARC record in an OPAC or an EAD finding aid maintained on a WWW server) or contain internally embedded descriptive metadata or both. Multiple instances of both external and internal descriptive metadata may be included in the descriptive metadata section.

• 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 object derives, and information regarding the provenance of the files comprising the digital object (i.e., master/derivative file relationships, and migration/transformation information). As with descriptive metadata, administrative metadata may be either external to the METS document or encoded internally.

• File Groups - The file group section lists all files comprising all electronic versions of the digital object. File group elements may be nested, to provide for subdividing the files by object version.

• 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.

• Behavior - A behavior section can be used to associate executable behaviors with content in the METS object. A behavior section has an interface definition element that represents an abstract definition of the set of behaviors represented by a particular behavior section. A behavior section also has a behavior mechanism which is a module of executable code that implements and runs the behaviors defined abstractly by the interface definition.

The Library of Congress provides maintenance services both PREMIS and METS working closely with national and international organizations.