The Dublin Core metadata element set is a standard for cross-domain information resource description. It provides a simple and standardised set of conventions for describing things online in ways that make them easier to find. Dublin Core is widely used to describe digital materials such as video, sound, image, text, and composite media like web pages. Implementations of Dublin Core typically make use of XML and are Resource Description Framework based. Dublin Core is defined by NISO Standard Z39.85-2007
The Dublin Core Metadata Initiative (DCMI) is an organization providing an open forum for the development of interoperable online metadata standards that support a broad 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 widespread acceptance of metadata standards and practices.
Simple Dublin Core
The Simple Dublin Core Metadata Element Set (DCMES) consists of 15 metadata elements:
- Title
- Creator
- Subject
- Description
- Publisher
- Contributor
- Date
- Type
- Format
- Identifier
- Source
- Language
- Relation
- Coverage
- Rights
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 .
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.
Element 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 that 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 (e.g., a 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 the standard expression of a date). If an encoding scheme is not understood by an application, the value may still be useful to a human reader.
DCMI also maintains a small, general vocabulary recommended for use within the element Type. This vocabulary currently consists of 12 terms :
- Collection
- Dataset
- Event
- Image
- InteractiveResource
- MovingImage
- PhysicalObject
- Service
- Software
- Sound
- StillImage
- Text
