Dublin Core is an initiative to create a digital "library card catalog" for the Web. Dublin Core is made up of 15 metadata (data that describes data) elements that offer expanded cataloging information and improved document indexing for search engine programs.
The 15 metadata elements used by Dublin Core are: title (the name given the resource), creator (the person or organization responsible for the content), subject (the topic covered), description (a textual outline of the content), publisher (those responsible for making the resource available), contributor (those who added to the content), date (when the resource was made available), type (a category for the content), format (how the resource is presented), identifier (numerical identifier for the content such as a URL), source (where the content originally derived from), language (in what language the content is written), relation (how the content relates to other resources, for instance, if it is a chapter in a book), coverage (where the resource is physically located), and rights (a link to a copyright notice).
Two forms of Dublin Core exist: Simple Dublin Core and Qualified Dublin Core. Simple Dublin Core expresses elements as attribute-value pairs using just the 15 metadata elements from the Dublin Core Metadata Element Set. Qualified Dublin Core increases the specificity of metadata by adding information about encoding schemes, enumerated lists of values, or other processing clues. While enabling searches to be more specific, qualifiers are also more complex and can pose challenges to interoperability.
Each method of recording or transferring Dublin Core metadata has its plusses and minuses. HTML, XML, RDF, and relational databases are among the more common methods.
The Dublin Core Metadata Initiative began in 1995, taking its name from the location of the original workshop, Dublin, Ohio. It has since become international in scope and has representatives from more than 20 countries now contributing. Dublin Core has always held that resource discovery should be independent from the medium of the resource. So, while Dublin Core targets electronic resources, it aims to be flexible enough to help in searches for more traditional formats of data too. Web sites, though, are the most common users of Dublin Core.