An Introduction to Dublin Core
October 25, 2000
Simplicity and Utility are Keys to the Future of the Web
The Web is an important universal information tool, embracing vast stores of information with many purposes, multiple disparate sources, and quite a few unpredictable users. There is a clear need to improve access to this mass of information and for the development of better search, retrieval, and organizational tools.
Metadata (data about data) is a fundamental part of the solution to these challenges. Effective use of metadata requires three things: a set of commonly-understood terms to describe the content of information resources (semantics); a standard grammar for connecting those terms in meaningful metadata sentences; and a framework that allows us to exchange and recombine those metadata sentences across different applications and subjects. These three elements -- standardized semantics, a definitive syntax, and a framework for exchange -- provide an architecture for resource description that can work across all subject areas on the Web.
Developing a single and complete vocabulary for resource description is a difficult problem. Tackling this effort in a flexible fashion, however, allows for an incremental solution with manageable constituent parts. Lego, the familiar building blocks of childhood, is the perfect metaphor for describing how metadata can be incorporated into the Web to support the management of information. Lego blocks come in themes, consisting of simple colored bricks created with consistent, engineered dimensions that allow them to snap together with a satisfying click.
The Dublin Core Metadata Element Set (DCMES) can be viewed as the common semantic building block of Web metadata. Its 15 broad categories (elements) are useful for creating simple, easy-to-understand descriptions for most information resources. Most communities need additional semantics to fully describe their resources, however. So, just as simple Lego blocks can be combined to form complex structures, various modules of metadata can be combined to form more complex descriptions. The DCMES is the basic block, but other chunks of metadata can be combined with it to form richer descriptions.
The basic element set is intended to capture most of the fundamental descriptive categories necessary to promote effective search and retrieval. Additional building blocks can be created to provide modular chunks of metadata that can be built into richer descriptions for information resources. So, just as Lego blocks of various shapes can be snapped together to form undersea exploration themes, or recombined to create spaceships or medieval castles, chunks of metadata can be combined and recombined to meet the functional requirements of different applications.
Metadata Modularity on the Web
The Dublin Core Metadata Initiative provides a forum for the definition of semantics, both for a general description core and for subject-specific extensions. How can these vocabularies be integrated into a functional architecture? Dublin Core metadata can be carried in HTML, XML, and RDF. The latter, the Resource Description Framework, builds on the World Wide Web Consortium's (W3C) effort to design an architecture for metadata on the Web. RDF supports many different metadata needs of vendors and information providers. If Dublin Core Metadata Element Set can be thought of as a Lego that is common to many sets, RDF is the engineering standard that enables that satisfying click when the blocks are snapped together.
RDF is part of an infrastructure that will support the combination of Dublin Core modules into larger, more expressive metadata structures that will work with one another. Further, applications should be able to mix metadata from other semantic standards expressed in RDF as well. Just as different Lego sets express undersea, outer space or medieval castle themes, RDF can enable snapping together modules that support metadata themes for education, government, or commercial purposes, all working together in the same architecture. For example, members of the RSS community have recently been advocating RDF as a powerful, modular means of combining semantics defined by Dublin Core with additional vocabularies (syndication, aggregation, threading) to produce effective site summaries and syndication services. an example of how this might be used as a modular means for combining semantics is the following.
<?xml version="1.0"?> <rdf:RDF xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#" xmlns:rss="http://purl.org/rss/1.0/" xmlns:dc="http://purl.org/dc/elements/1.1/"> <rss:channel rdf:about="http://www.xml.com/xml/news.rss"> <rss:title>XML.com</rss:title> <rss:link>http://xml.com/pub</rss:link> <dc:description> XML.com features a rich mix of information and services for the XML community. </dc:description> <dc:subject>XML, RDF, metadata, information syndication services</dc:subject> <dc:identifier>http://www.xml.com</dc:identifier> <dc:publisher>O'Reilly & Associates, Inc.</dc:publisher> <dc:rights>Copyright 2000, O'Reilly & Associates, Inc.</dc:rights> </rss:channel> </rdf:RDF>
The Dublin Core Metadata Initiative
Creating the semantic building blocks of the Web
The mission of the Dublin Core Metadata Initiative (DCMI) is to make it easier to find resources using the Internet through the following activities:
- Developing metadata standards for resource search and retrieval across different subject areas
- Defining frameworks for the interoperability of metadata sets
- Facilitating the development of community- or subject-specific metadata sets that work within these frameworks
The Dublin Core metadata element set (or the basic Lego brick) is intended to support cross-subject search and retrieval. It can be thought of as a simplistic or pidgin metadata language that helps the user navigate through disparate subjects, languages, and cultures. Adoption of the Dublin Core by governments, libraries, museums, archives, publishers, environmental science repositories, print and e-print archives, to name a few, testifies to its success in this role. There are emerging applications in the commercial sector, as well, with health care organizations and financial industries using the Dublin Core as the basis for organizing and exchanging information.
Part of the mission of DCMI is to provide a vendor-neutral forum for the development of additional vocabularies that are interoperable within the broader architecture of the Dublin Core and other Web metadata schemas in general. At the recent 8th Dublin Core metadata workshop in Ottawa, Canada, a special interest group formed around the exploration of metadata issues that are of particular interest to the business community. The provisional charter for this group is to provide a forum:
- To investigate metadata schemas used in commercial business models
- To promote the use of Dublin Core in internal and cross-company business environments;
- To identify business sectors and commercial resources (e.g. information, services, catalogs, products) that could benefit from the use of the DC standard;
- To highlight within the DC Community the commercial ramifications of DC developments;
- To discuss the possible expansion of Dublin Core to accommodate information vital to commercial requirements and uses.
Interested parties may subscribe to the discussion list.
Other Activities of the Initiative
In addition to providing international forums for the development of vendor-neutral vocabularies, the DCMI is promoting the development of tools and infrastructure to support high quality metadata applications on the Internet, including
- a semantic registry to store and search declared meanings and their relationships to other meanings; and
- an open source software repository to provide the tools for creating, editing, managing, and navigating metadata.
The registry activity is a fundamental part of both the management and use of metadata, allowing, in the short term, the registration and public disclosure of metadata schemas at a granularity that allows management and discovery of descriptors at the element level. Metadata schema developers will use the registry to discover what other applications have adopted. Users will be able to identify the precise definitions of elements, and applications will be able to resolve machine-processable mappings among different schemas, further enhancing the prospects for Web-wide metadata interoperability.
By supporting the development of such tools in an open source environment, the DCMI hopes to promote broad contribution of value by the community at large.
While the Dublin Core began with the goal of developing a simple, interoperable, extensible, consensus-built metadata standard, it has evolved beyond a basic element set to embrace new communities and subject areas. The Dublin Core Metadata Initiative has become a home for a broad spectrum of subject experts and metadata practitioners, built on community trust and open consensus building, and motivated by a desire to build a Web of greater coherence.