Metadata: The Foundations of Resource Description

Stuart Weibel
Office of Research, OCLC Online Computer Library Center, Inc.

D-Lib Magazine, July 1995

This paper is an abbreviated version of the Summary Report of the OCLC/NCSA Metadata Workshop . It sets forth a proposal for the content of a simple resource description record (the Dublin Core Metadata Element Set) and outlines a series of further steps to advance the standards for the description of networked information resources.

  • Introduction
  • Underlying Assumptions
  • Implementations
  • Next Steps
  • References

  • Introduction

    The explosive growth of interest in the Internet in recent years has created a digital extension of the academic research library for certain kinds of materials. Valuable collections of texts, images and sounds from many scholarly communities -- collections that may even be the subject of state-of-the-art discussions in these communities--now exist only in electronic form and may be accessible from the Internet. Knowledge regarding the whereabouts and status of this material is often passed on by word of mouth among members of a given community. For outsiders, however, much of this material is so difficult to locate that it is effectively unavailable.

    Why is it so difficult to find items of interest on the Internet or the World Wide Web? A number of well-designed locator services, such as Lycos [] , are now available that automatically index many of the resources available on the Web and maintain up-to-date databases of locations. But indexes are most useful in small collections within a given domain. As the scope of their coverage expands, indexes succumb to problems of large retrieval sets and problems of cross disciplinary semantic drift. Richer records, created by content experts, are necessary to improve search and retrieval. Formal standards such as the TEI Header and MARC cataloging) will provide the necessary richness, but such records are time consuming to create and maintain, and hence may be created for only the most important resources.

    An alternative solution that promises to mediate these extremes involves the creation of a record that is more informative than an index entry but is less complete than a formal cataloging record. If only a small amount of human effort were required to create such records, more objects could be described, especially if the author of the resource could be encouraged to create the description. And if the description followed an established standard, only the creation of the record would require human intervention; automated tools could discover these descriptions and collect them.

    Can a simple metadata record be defined that sufficiently describes a wide range of electronic objects? The Online Computer Library Center (OCLC) and the National Center for Supercomputing Applications (NCSA) convened the invitational Metadata Workshop on March 1-3, 1995, in Dublin, Ohio to address this issue. Fifty-two librarians, archivists, humanities scholars and geographers, as well as standards makers in the Internet, Z39.50 and Standard Generalized Markup Language (SGML) communities, met to identify the scope of the problem, to achieve consensus on a list of metadata elements that would yield simple descriptions of data in a wide range of subject areas, and to lay the groundwork for achieving further progress in the definition of metadata elements that describe electronic information.


    Goals of the workshop included fostering a common understanding of the problems and potential solutions among the stakeholders and promoting a consensus on a core set of metadata elements to describe networked resources.


    Since the Internet contains more information than professional abstractors, indexers and catalogers can manage using existing methods and systems, it was agreed that a reasonable alternative way to obtain usable metadata for electronic resources is to give authors and information providers a means to describe the resources themselves. The major task of the Metadata Workshop was to identify and define a simple set of elements for describing networked electronic resources. To make this task manageable, it was limited in two ways. First, only those elements necessary for the discovery of the resource were considered. It was believed that resource discovery is the most pressing need that metadata can satisfy, and one that would have to be satisfied regardless of the subject matter or internal complexity of the object.

    Secondly, the discussion was further restricted to the metadata elements required for the discovery of what were called document-like objects, or DLOs by the workshop participants. It was believed that DLOs are still the most common type of resource sought in the Internet and that whatever solution could be proposed for DLOs could be extended to other kinds of resources. More importantly, the likelihood of making progress on this challenging problem would be increased if attention could initially be restricted to something familiar.

    DLOs were not rigorously defined, but were understood by example. For example, an electronic version of a newspaper article or a dictionary is a DLO, while an unannotated collection of slides is not. Of course, the crux of the problem is that in a networked environment, DLOs can be arbitrarily complex because they can consist of text with callouts to images, audio or video clips, or to other hypertext documents. The Metadata Workshop participants made no attempt to limit the complexity of DLOs, except to say that the intellectual content of a DLO is primarily text, and that the metadata required for describing DLOs will bear a strong resemblance to the metadata that describes traditional printed texts.

    As a result of the restricted focus of the workshop, certain issues required for a complete description of DLOs, such as cost, archival status and copyright information, were eliminated from the scope of the discussion. Elements required for the description of objects other than DLOs, such as the elements required for the description of complex geological strata in a geospatial resource, were also beyond the scope of the discussion. The goal was to define a core set of metadata elements that would allow authors and information providers to describe their work and to facilitate interoperability among resource discovery tools. But because the core elements do not yield a complete description of objects in a networked environment, careful consideration was also given to mechanisms for extending the element set.

    The primary deliverable from the workshop was a set of thirteen metadata elements, named the Dublin Core Metadata Element Set (or Dublin Core, for short). The Dublin Core was proposed as the minimum number of metadata elements required to facilitate the discovery of document-like objects in a networked environment such as the Internet. The syntax was deliberately left unspecified as an implementation detail. The semantics of these elements was intended to be clear enough to be understood by a wide range of users.

    Below is a brief description of the elements in the Dublin Core Dublin Core Element Description

    To make this discussion concrete, consider an electronic a record created with the relevant portions of the Dublin Core, and a sample syntax, that describes an electronic version of Maya Angelou's poem "On the Pulse of Morning". This description is based on a record created by the University of Virginia Library's Electronic Text Center. (For a description of that project, see Gaynor [Gaynor] .)

    Underlying Assumptions

    The discussions at the Metadata Workshop revealed several principles that should guide the further development of the element set. Adherence to these principles increases the likelihood that the core element set will be kept as small as possible, that the meanings of the elements will be understood by most users, and that the element set will be flexible enough for the description of resources in a wide range of subject areas. These principles are intrinsicality, extensibility, syntax independence, optionality, repeatability, and modifiability.


    The Dublin Core concentrates on describing intrinsic properties of the object. Intrinsic data refer to the properties of the work that could be discovered by having the work in hand, such as its intellectual content and physical form. This is distinguished from extrinsic data, which describe the context in which the work is used. For example, the "Subject" element is intrinsic data, while transaction information such as cost and access considerations are extrinsic data. The focus on intrinsic data in no way demeans the importance of other varieties of data, but simply reflects the need to keep the scope of deliberations narrowly focussed.


    In addition to its use in dealing with extrinsic data, extension mechanisms will allow the inclusion of intrinsic data for objects that cannot be adequately described by a small set of elements.

    Extensibility is important because users may wish to add extra descriptive material for site-specific purposes or specialized fields. In addition, the specification of the Dublin Core itself will change over time, and the extension mechanism will allow revisions while maintaining some backward compatibility with the originally defined element set.

    Syntax Independence

    Syntactic bindings are avoided because it is too early to propose formal definitions and because the Dublin Core is intended to be eventually used in a range of disciplines and application programs.


    All the elements are optional. The Dublin Core may eventually be applied to objects for which some elements have no meaning (who is the author of a satellite image?). It also seems counterproductive to mandate complex descriptions if the creators of the content are expected to provide the descriptive material. A simple description is better than no description at all.


    All elements in the Dublin Core are repeatable. For example, multiple author elements would be used when a resource has multiple authors.


    Each element in the Dublin Core has a definition that is intended to be self-explanatory. However, it is also necessary that the definitions of the elements satisfy the needs of different communities. This goal is accomplished by allowing each element to be modified by an optional qualifier. If no qualifier is present, the element has its common-sense meaning; otherwise, the definition of the element is modified by the value of the qualifier.

    Qualifiers will be typically derived from well-known conventions in the library community or from the field of knowledge appropriate to the resource. Qualifiers are important because they give the Dublin Core a mechanism for bridging the gap between casual and sophisticated users. For example, the data in the Subject element consists of any word or phrase that describes the object's content. However, a professional cataloger may wish to supply the name of the authoritative source from which the subject terms are taken. In such a case, the element may be written as Subject (scheme=LCSH) , indicating that the subject terms are taken from the Library of Congress Subject Headings.


    One of the goals of the OCLC/NCSA Metadata Workshop was to promote prototype resource description projects based on a common model of resource description. A number of Metadata Workshop conferees represent organizations that have ongoing activities or are starting activities that will be influenced by the results of the workshop. These include:

    Next Steps

    Refinement and standardization of the metadata element set defined in this document will be an ongoing, dynamic process involving many stakeholder communities. No single forum will suffice to air all concerns and no single standard can be expected to accommodate the needs of all communities. The problem must be divided into manageable chunks and the process must engage the relevant stakeholder communities. Implicit in the present activity is the proposition that there are core elements common to many object types, and that a simple, extensible framework of such elements can be defined to support more complete resource descriptions.

    The initial objective--the specification of elements for the discovery of document-like objects--can be extended in a variety of directions:

    OCLC and NCSA will establish a workshop series to address aspects of this agenda. A Metadata Workshop Steering Committee will be established to define topics and assure appropriate representation of stakeholders. Design groups of perhaps a dozen or fewer individuals will be solicited to prepare discussion papers to focus workshop activities. Participants will be invited based on their publicly evident accomplishments in relevant areas or by reviewed application. Workshops will be limited to 50 or fewer participants and conducted in roughly the style of the March 1995 Workshop.

    Other work will be done in coordination with IETF working group on Uniform Resource Identifiers (URIs) to assure that the results can be integrated into the emerging protocols for resource location and persistent naming.

    Finally, active promotion of results will be carried out by establishing liaison with formal associations of stakeholders. In the library community, MARC standards evolve under the guidance of the Machine-Readable Bibliographic Information Committee (MARBI), composed of representatives of the Library of Congress and other stakeholders in the library community. A close relationship should be sustained between this committee and the Metadata Work Group. Relationships should also be established with publishers, document vendors, SGML vendors and theoreticians working on the problem of text encoding. Other communities also have requirements that must be accommodated in any framework for resource description. These communities include the GIS community, government information providers and business communication groups.


    Network Development and MARC Standards, Office, ed. 1994. USMARC Format for Bibliographic data. 1994. Washington, DC: Cataloging Distribution Service, Library of Congress.

    Sperberg-McQueen, C. M., and Leu Burnard, ed. 1994. Guidelines for Electronic Text Encoding and Interchange. Chicago and Oxford: Text Encoding Initiative.

    Gaynor, Edward. 1994. "Cataloging Electronic Texts: The University of Virginia Library Experience." Library Resources and Technical Services 38(4): 403-413 (October 1994).

    Copyright © 1995 OCLC