Dublin Core Metadata
The Dublin Core set of metadata elements provides a small and fundamental group of text elements through which most resources can be described and catalogued. Using only 15 base text fields, a Dublin Core metadata record can describe physical resources such as books, digital materials such as video, sound, image, or text files, and composite media like web pages. Metadata records based on Dublin Core are intended to be used for cross-domain information resource description and have become standard in the fields of library science and computer science. Implementations of Dublin Core typically make use of XML and are Resource Description Framework based.
Dublin Core is defined by ISO through ISO Standard 15836, and NISO Standard Z39.85-2007.
The "Dublin" in the name refers to Dublin, Ohio, U.S., where the work originated from an invitational workshop (the OCLC/NCSA Metadata Workshop) hosted in 1995 by Online Computer Library Center (OCLC), a library consortium based there.("NCSA" stands for the National Center for Supercomputing Applications.)
The "Core" refers to the fact that the metadata element set is a basic but expandable "core" list.
The semantics of Dublin Core were established and are maintained by an international, cross-disciplinary group of professionals from librarianship, computer science, text encoding, museums, and other related fields of scholarship and practice.
The Dublin Core Metadata Initiative (DCMI) incorporated as an independent entity (separating from OCLC) in 2008 that provides an open forum for the development of interoperable online metadata standards for a broad range of purposes and of business models. DCMI's activities include consensus-driven working groups, global conferences and workshops, standards liaison, and educational efforts to promote widespread acceptance of metadata standards and practices.
Levels of the standard
The Dublin Core standard includes two levels: Simple and Qualified. Simple Dublin Core comprises 15 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.
Simple Dublin Core
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.
Example of Code
Qualified Dublin Core
Subsequent to the specification of the original 15 elements, an ongoing process to develop exemplary terms extending or refining the Dublin Core Metadata Element Set (DCMES) was begun. The
additional terms were identified, generally in working groups of the Dublin Core Metadata Initiative, and judged by the DCMI Usage Board to be in conformance with principles of good practice for the qualification of Dublin Core metadata elements.
Elements refinements make the meaning of an element narrower or more specific. A refined element shares the meaning of the unqualified element, but with a more restricted scope. The guiding principle for the qualification of Dublin Core elements, colloquially known as the Dumb-Down Principle,  states that an application which does not understand a specific element refinement term should be able to ignore the qualifier and treat the metadata value as if it were an unqualified (broader) element. While this may result in some loss of specificity, the remaining element value (without the qualifier) should continue to be generally correct and useful for discovery.
In addition to element refinements, Qualified Dublin Core includes a set of recommended encoding schemes, designed to aid in the interpretation of an element value. These schemes include controlled vocabularies and formal notations or parsing rules. A value expressed using an encoding scheme may thus be a token selected from a controlled vocabulary (for example, a term from a classification
system or set of subject headings) or a string formatted in accordance with a formal notation (for example, "2000-12-31" as the standard expression of a date). If an encoding scheme is not understood by an application, the value may still be useful to human reader.
Audience, Provenance and RightsHolder are elements, but not part of the Simple Dublin Core 15 elements. Use Audience, Provenance and RightsHolder only when using Qualified Dublin Core. DCMI also maintains a small, general vocabulary recommended for use within the element Type. This vocabulary 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, it is important to note that Dublin Core concepts and semantics are designed to be syntax independent, are equally applicable in a variety of contexts, as long as the metadata is in a form suitable for interpretation both by machines and
by human beings.
The Dublin Core Abstract Model provides a reference model against which particular DC encoding guidelines can be compared, independent of any particular encoding syntax. Such a reference model allows implementers to gain a better understanding of the kinds of descriptions they are trying to encode and facilitates the development of better mappings and translations between different syntaxes.
One Document Type Definition based on Dublin Core is the Open Source Metadata Framework (OMF) specification. OMF is in turn used by Rarian (superseding ScrollKeeper), which is used by the GNOME desktop and KDE help browsers and the ScrollServer documentation server. PBCore is also based on Dublin Core. The Zope CMF's Metadata products, used by the Plone, ERP5, the Nuxeo CPS Content management systems, SimpleDL, and FedoraCommons also implement Dublin Core.
DCMI also maintains a list of projects using Dublin Core on its website.
External linksDublin Core Metadata InitiativeOfficial usage guideDublin Core Metadata RegistryDublin Core Metadata Initiative Publishes DCMI Abstract Model (Cover Pages, March 2005)