PREMIS (PREservation Metadata: Implementation Strategies) is an international working group concerned with developing metadata for use in digital preservation.
In 2003 the Online Computer Library Center (OCLC) and Research Libraries Group (RLG) established the PREMIS working group, which consisted of a multi-national roster of more than thirty representatives from the cultural, government, and private sectors, in order to define implementable, core preservation metadata, with guidelines/recommendations for management and use.[1] PREMIS was “charged to define a set of semantic units that are implementation independent, practically oriented, and likely to be needed by most preservation repositories”.[2]
In May 2005, PREMIS released Data Dictionary for Preservation Metadata: Final Report of the PREMIS Working Group. This 237-page report includes: PREMIS Data Dictionary 1.0: a comprehensive, practical resource for implementing preservation metadata in digital archiving systems; accompanying report (providing context, data model, assumptions); special topics, glossary, usage examples; set of XML schema which was developed to support use of the Data Dictionary.[3] Version 2.0 of PREMIS was released in March 2008.[4]
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The PREMIS data model consists of five interrelated entities: Intellectual, Object, Event, Agent, and Rights with each semantic unit mapped to one of these areas.[5]
An intellectual entity is a set of content that constitutes a discrete, coherent intellectual unit, such as a book or a database. These may be compound objects containing other intellectual entities and may have multiple digital representations.[6] Descriptive metadata is usually applied at this level; given the proliferation of competing schemes, the working group did not define any further descriptive semantic units[7] and allowed for interoperability through “extension containers” (containers hold a related group of semantic units) that can be used for external schemes.[6]
Most of the semantic units listed in the data dictionary relate to object and event entities, the former being further divided into three subtypes of file, bitstream, and representation. A file is the level at which most end users are used to working, a “named and ordered sequence of bytes that is known by an operating system.” It includes a variety of file system attributes, rendering it understandable by an operating system, encompassing bitstreams, which are “contiguous or non-contiguous data within a file that has meaningful common properties for preservation purposes.” A representation is, in a sense, the “highest level” of this model, for it may encompass several files in order to properly render the structure and content of an intellectual entity. Not all repositories will be concerned with preserving representations,[8] depending on their purpose and the curatorial body’s need to preserve what might be considered the entity’s digital “intrinsic value.” Furthermore, intellectual entities may have multiple representations within a repository. Events interrelate with objects insofar as they involve actions that have an effect on them or agents ("a person, organization, or software...associated with Events...or with Rights attached to an object") associated with the object.[6]
Finally, the inclusion of rights entities responds to an increased awareness of and concern for the legal requirements of copyright and licensing. It also includes information about the specific actions permitted; for example, semantic unit 4.1.6.1, act, “the action the preservation repository is allowed to take,” includes such suggested values as replicate, migrate, and delete.[9]
PREMIS data dictionary entries include twelve attribute fields, not all of which are applied to every semantic unit (analogous to an "element" in other metadata schemes). In addition to the name and definition of the unit, the fields record such things as rationale for including the unit, usage notes, and examples of how the value might be filled in. Four of the attributes - object category, applicability, repeatability, and obligation - are linked, as the last three are defined for each of the object entity levels of file, bitstream, and representation. The dictionary is hierarchical; some semantic units are contained within others. For example, 1.3 preservationLevel, includes four semantic components, such as 1.3.1 preservationLevelValue and 1.3.2 preservationLevelRole.[10]