Librarians are increasingly called upon not only to collect information in electronic form but also to organize it into digital libraries. The materials may be created and held locally, or they may be created and accessed in a distributed fashion as a virtual library. Digital libraries can provide material on a variety of topics, from children’s games to high-energy physics. Their scope may be local, national, or even international; the audience may be a small group with specialized interests or the broader public. Essential to the successful implementation and use of any digital library is the organization of that library, either directly or indirectly, by one or more knowledge organization systems (KOS).

The term knowledge organization systems is intended to encompass all types of schemes for organizing information and promoting knowledge management. Knowledge organization systems include classification and categorization schemes that organize materials at a general level, subject headings that provide more detailed access, and authority files that control variant versions of key information such as geographic names and personal names. Knowledge organization systems also include highly structured vocabularies, such as thesauri, and less traditional schemes, such as semantic networks and ontologies. Because knowledge organization systems are mechanisms for organizing information, they are at the heart of every library, museum, and archive.

The knowledge organization system used in a particular situation may be borrowed from the library tradition, such as the Library of Congress Classification Schedule, or from commerce, such as the Yahoo categories, or it may be developed locally. The KOS may be applied to metadata records for each resource, embedded in metatags, or separated from the digital library resources as part of the access mechanism. Regardless of its location with respect to the resource, its origin, or its type, the KOS has a single purpose: to organize content to support retrieval of relevant items from a digital library collection.

The first section of this report defines the general characteristics of KOSs, with emphasis on their connection to a particular view of the world. The historic origins and uses of KOSs, in libraries and in other information management environments, are described. Various types of KOSs are discussed.

Section 2 provides examples of how knowledge organization systems can be used to enhance digital libraries in a variety of disciplines. It describes how a KOS can be used to link a digital resource to related material. The KOS can be used directly or indirectly to provide more descriptive records for entities in the digital resource. Finally, the KOS can provide access not only to a descriptive record but also to location information about a relevant physical object.

Section 3 discusses how KOSs can be used to provide disparate communities with access to digital library resources. This can be done by using a KOS to provide alternate subject access, to add a new mode of access to the digital library (for example, visual or geographic in addition to textual), to provide multilingual access, or to support free-text searching.

The report concludes with a discussion of issues to consider when using KOSs with digital libraries. It provides a framework for the design, planning, implementation, and maintenance of KOSs in digital library environments.