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Dublin Core refers to the metadata standard created by the Dublin Core Metadata Initiative (DCMI). The "core" in Dublin Core is used to describe "core" information properties of digital materials. The "Dublin" part refers to Dublin, Ohio where discussions for the standard began in 1995 at OCLC. The "Core" in Dublin Core refers to metadata elements, a basic but expandable "core" list of attributes used to describe digital items in a methodical, standard way. Dublin Core refers to "fifteen metadata elements for resource description in a cross-disciplinary information environment" which provide a simple set of conventions for describing items and thus make them easier to find.
DC is widely used to describe digital materials such as video, sound, image, text, and composite media like web pages. Each Dublin Core element is optional and may be repeated. Dublin Core has established standard ways to refine elements and encourage the use of encoding and vocabulary schemes. There is no prescribed order in Dublin Core for presenting or using the elements. Implementations of DC make use of XML and the Resource Description Framework (See NISO Standard Z39.85-2007). The semantics of Dublin Core were established and are maintained by an international, cross-disciplinary group of professionals from librarianship, computer science, text encoding, the museum community, and other related fields. The Dublin Core Metadata Initiative is an organization and open forum developing interoperable metadata standards to support a range of purposes and business models. DCMI's activities include consensus-driven working groups, global conferences and workshops, standards liaison, and educational efforts to promote wide acceptance of metadata standards and practices.
Simple and Qualified DC
The Dublin Core standard includes two levels: Simple and Qualified. Simple Dublin Core comprises fifteen elements; Qualified Dublin Core includes three additional elements (Audience, Provenance and RightsHolder), as well as a group of element refinements (also called qualifiers) that refine the semantics of the elements in ways that may be useful in resource discovery.
The Simple Dublin Core Metadata Element Set (DCMES) consists of 15 metadata elements:
Each Dublin Core element is optional and may be repeated. The DCMI has established standard ways to refine elements and encourage the use of encoding and vocabulary schemes. There is no prescribed order in Dublin Core for presenting or using the elements. Full information on element definitions and term relationships can be found in the Dublin Core Metadata Registry Dublin Core Metadata Registry.
Qualified Dublin Core
After the original 15 elements were specified, an ongoing process extended the Metadata Element Set (DCMES). Additional terms were identified in working groups and judged by the Usage Board to conform with principles of good practice for Dublin Core metadata elements. The goal is to make an element narrower or more specific; a refined element shares meaning of the unqualified element but in a more restricted way. The guiding principle for qualification of elements - known as the Dumb-Down Principle - is that an application that does not understand a specific refinement should ignore it and treat it as an unqualified element. While this results in loss of specificity, the remaining element (without qualifier) is adequate for discovery. In addition to refinements, Qualified Dublin Core includes a set of recommended encoding schemes designed to aid in interpretation. A value expressed using an encoding scheme may be a token selected from a controlled vocabulary (e.g., term from a classification system or set of subject headings) or a string formatted in accordance with a formal notation (e.g., "2000-12-31" as standard expression of a date). If encoding is not understood by computers, it may be useful to use human readers. DCMI maintains a small vocabulary recommended for use within element Type; this currently consists of 12 terms.
Syntax choices for DC metadata depend on a number of variables, and "one size fits all" prescriptions rarely apply. When considering an appropriate syntax and vocabulary in your records, remember that Dublin Core's concepts and semantics are designed to be syntax independent and are equally applicable in a variety of contexts. As long as the metadata are in a form that is suitable for interpretation by machines and human beings, it can be in any form the creator envisions. Dublin Core's Abstract Model provides a good model against which particular encoding guidelines can be compared, independent of any particular encoding syntax. Good reference models allow implementors to gain a better understanding of the kinds of descriptions they are trying to encode and facilitates the development of better mapping, and translations between different syntaxes.