Introduction

This document presents the results of a process to develop exemplary qualifiers for the Dublin Core Metadata Element Set (DCMES). The qualifiers listed here were identified in element-specific working groups of the Dublin Core Metadata Initiative (DCMI) and judged by the DCMI Usage Committee to be in conformance with principles of good practice for the qualification of Dublin Core metadata elements. Working groups proposed candidate qualifiers judged likely to be of widespread use (and hence to increase the likelihood of interoperability among applications) and these proposals were subsequently debated and balloted by the DCMI Usage Committee.

In determining the makeup of these qualifiers, preference was given to vocabularies, notations, and terms already maintained by established agencies. It should be emphasized that the list of externally-maintained vocabularies identified here is a preliminary list. There are many more controlled vocabularies or classification systems that are not identified here. The DCMI welcomes suggestions concerning additional existing standards that might serve as qualifiers.

Inevitably, there will be situations where an agent or client will encounter DCMES descriptions that use unfamiliar qualifiers developed by implementors for specialized local or domain-specific needs. The useful interpretation of such a DCMES description will depend on the ability of an application to ignore the unknown qualifiers and fall back on the broader meaning of the element in its unqualified form. The guiding principle for the qualification of Dublin Core elements, colloquially known as the Dumb-Down Principle, is that a client should be able to ignore any qualifier and use the description as if it were unqualified. 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.

It is expected that implementors will develop additional qualifiers for use within local applications or specific domains. Such qualifiers may not be understood by other applications. However, qualifiers that conform to the principles of qualification defined here are more likely to be reusable by other communities within the broader context of cross-domain discovery.

At the time of the ratification of this document, the DCMI recognizes two broad classes of qualifiers:

• Element Refinement. These qualifiers 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. A client 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. The definitions of element refinement terms for qualifiers must be publicly available.
• Encoding Scheme. These qualifiers identify schemes that 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 will 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., "2000-01-01" as the standard expression of a date). If an encoding scheme is not understood by a client or agent, the value may still be useful to a human reader. The definitive description of an encoding scheme for qualifiers must be clearly identified and available for public use.

All of the qualifiers listed in this document fall into one of these two categories. Additional qualifier categories may evolve over time and with implementation experience. Proposed qualifiers which appeared to the DCMI Usage Committee to fall outside of these categories, or which fell short in some other respect (e.g., clarity of definition), will become the focus of further discussion and be reconsidered for approval in the future.

The qualifiers listed here do not constitute a closed set, designed to meet all of the descriptive needs of implementors. Rather, they form the foundation for a larger body of qualifiers that will evolve as additional qualifiers are developed by various communities and submitted to the DCMI Usage Committee for review and approval. Implementors may deploy these qualifiers with confidence that they conform to the Dumb-Down Principle, and are encouraged to use these qualifiers as examples to guide development of local qualifiers for Dublin Core metadata elements.

Summary of Qualifiers (non-normative)

This summary of the qualifiers is provided for the convenience of users. The reference definitions are to be found below.

Properties of Dublin Core Qualifiers

Dublin Core qualifiers have the following properties:

• Name: The unique token assigned to the qualifier.
• Label: The human-readable label assigned to the qualifier.
• Definition: A statement that represents the concept and essential nature of the qualifier.
• Comment: Additional information associated with the qualifier (if available).
• See Also: A link to more information about the qualifier (if available).

Note that the properties of qualifiers -- in particular the terms Name and Label -- differ with respect to those defined for the Dublin Core Metadata Element Set Version 1.1. These changes reflect a decision to bring Dublin Core schema terminology in line with terminology in the XML community to promote easier integration of Dublin Core schemas in XML and RDF environments.

Multiple Language Encodings of Dublin Core Entities

Dublin Core qualifiers will be expressed in languages other than English. A single invariant token assigned to each qualifier -- the Name property -- stands for a given qualifier concept irrespective of the language in which it is defined. This token can be incorporated into a URI to form a unique identifier for the qualifier. All other properties of a qualifier (Label, Definition, Comment, and aspects of See Also as appropriate) can be translated from English into any other language.

All other properties of Dublin Core entities (Label, Definition, Comment, and aspects of See Also as appropriate) will be expressed in the language and character set of the translation.

Dublin Core Qualifiers

Title
The qualifiers below are recommended for the Title element.

Qualifiers that refine Title:

Alternative

Name: alternative
Label: Alternative
Definition: Any form of the title used as a substitute or alternative to the formal title of the resource.
Comment: This qualifier can include Title abbreviations as well as translations.

Subject
The qualifiers below are recommended for the Subject element.

Encoding Schemes for Subject:

LCSH

Name: LCSH
Label: LCSH
Definition: Library of Congress Subject Headings

MeSH

Name: MESH
Label: MeSH
Definition: Medical Subject Headings
See also: http://www.nlm.nih.gov/mesh/meshhome.html

DDC

Name: DDC
Label: DDC
Definition: Dewey Decimal Classification
See also:http://www.oclc.org/dewey/index.htm

LCC

Name: LCC
Label: LCC
Definition: Library of Congress Classification See also: http://lcweb.loc.gov/catdir/cpso/lcco/lcco.html

UDC

Name: UDC
Label: UDC
Definition: Universal Decimal Classification See also: http://www.udcc.org/

Description
The qualifiers below are recommended for the Description element.

Qualifiers that refine Description:

Table Of Contents

Name: tableOfContents
Label: Table Of Contents
Definition: A list of subunits of the content of the resource.

Abstract

Name: abstract
Label: Abstract
Definition: A summary of the content of the resource.

Date
The qualifiers below are recommended for the Date element.

Qualifiers that refine Date:

Created

Name: created
Label: Created
Definition: Date of creation of the resource.

Valid

Name: valid
Label: Valid
Definition: Date (often a range) of validity of a resource.

Available

Name: available
Label: Available
Definition: Date (often a range) that the resource will become or did become available.

Issued

Name: issued
Label: Issued
Definition: Date of formal issuance (e.g., publication) of the resource.

Modified

Name: modified
Label: Modified
Definition: Date on which the resource was changed.

Encoding Schemes for Date:

DCMI Period

Name: Period
Label: DCMI Period
Definition: A specification of the limits of a time interval.
See also: http://purl.org/dc/documents/dcmi-period

W3C-DTF

Name: W3CDTF
Label: W3C-DTF
Definition: W3C Encoding rules for dates and times - a profile based on ISO 8601
See also: http://www.w3.org/TR/NOTE-datetime

Resource Type
The qualifiers below are recommended for the Resource Type element.

Encoding Schemes for Resource Type:

DCMI Type Vocabulary

Name: DCMIType
Label: DCMI Type Vocabulary
Definition: A list of types used to categorize the nature or genre of the content of the resource.
See also: http://purl.org/dc/documents/dcmi-type-vocabulary

Format
The qualifiers below are recommended for the Format element.

Qualifiers that refine Format:

Extent

Name: extent
Label: Extent
Definition: The size or duration of the resource.

Medium

Name: medium
Label: Medium
Definition: The material or physical carrier of the resource.

Encoding Schemes for Format:

IMT

Name: IMT
Label: IMT
Definition: The Internet media type of the resource.
See also: http://www.isi.edu/in-notes/iana/assignments/media-types/media-types

Resource Identifier
The qualifiers below are recommended for the Resource Identifier element.

Encoding Schemes for Resource Identifier:

URI

Name: URI
Label: URI
Definition: A URI Uniform Resource Identifier
See also: http://www.ietf.org/rfc/rfc2396.txt

Language
The qualifiers below are recommended for the Language element.

Encoding Schemes for Language:

ISO 639-2

Name: ISO639-2
Label: ISO 639-2
Definition: ISO 639-2: Codes for the representation of names of languages.
See also: http://lcweb.loc.gov/standards/iso639-2/langhome.html

RFC 1766

Name: RFC1766
Label: RFC 1766
Definition: Internet RFC 1766 'Tags for the identification of Language' specifies a two letter code taken from ISO 639, followed optionally by a two letter country code taken from ISO 3166.
See also: http://www.ietf.org/rfc/rfc1766.txt

Relation
The qualifiers below are recommended for the Relation element.

Qualifiers that refine Relation:

Is Version Of

Name: isVersionOf
Label: Is Version Of
Definition: The described resource is a version, edition, or adaptation of the referenced resource. Changes in version imply substantive changes in content rather than differences in format.

Has Version

Name: hasVersion
Label: Has Version
Definition: The described resource has a version, edition, or adaptation, namely, the referenced resource.

Is Replaced By

Name: isReplacedBy
Label: Is Replaced By
Definition: The described resource is supplanted, displaced, or superceded by the referenced resource.

Replaces

Name: replaces
Label: Replaces
Definition: The described resource supplants, displaces, or supersedes the referenced resource.

Is Required By

Name: isRequiredBy
Label: Is Required By
Definition: The described resource is required by the referenced resource, either physically or logically.

Requires

Name: requires
Label: Requires
Definition: The described resource requires the referenced resource to support its function, delivery, or coherence of content.

Is Part Of

Name: isPartOf
Label: Is Part Of
Definition: The described resource is a physical or logical part of the referenced resource.

Has Part

Name: hasPart
Label: Has Part
Definition: The described resource includes the referenced resource either physically or logically.

Is Referenced By

Name: isReferencedBy
Label: Is Referenced By
Definition: The described resource is referenced, cited, or otherwise pointed to by the referenced resource.

References

Name: references
Label: References
Definition: The described resource references, cites, or otherwise points to the referenced resource.

Is Format Of

Name: isFormatOf
Label: Is Format Of
Definition: The described resource is the same intellectual content of the referenced resource, but presented in another format.

Has Format

Name: hasFormat
Label: Has Format
Definition: The described resource pre-existed the referenced resource, which is essentially the same intellectual content presented in another format.

Encoding Schemes for Relation:

URI

Name: URI
Label: URI
Definition: A URI Uniform Resource Identifier
See also: http://www.ietf.org/rfc/rfc2396.txt

Coverage
The qualifiers below are recommended for the Coverage element.

Qualifiers that refine Coverage:

Spatial

Name: spatial
Label: Spatial
Definition: Spatial characteristics of the intellectual content of the resoure.

Encoding Schemes for Spatial:

DCMI Point

Name: Point
Label: DCMI Point
Definition: The DCMI Point identifies a point in space using its geographic coordinates.
See also: http://purl.org/dc/documents/dcmi-point

ISO 3166

Name: ISO3166
Label: ISO 3166
Definition: ISO 3166 Codes for the representation of names of countries
See also: http://www.din.de/gremien/nas/nabd/iso3166ma/codlstp1/index.html

DCMI Box

Name: Box
Label: DCMI Box
Definition: The DCMI Box identifies a region of space using its geographic limits.
See also: http://purl.org/dc/documents/dcmi-box

TGN

Name: TGN
Label: TGN
Definition: The Getty Thesaurus of Geographic Names
See also: http://shiva.pub.getty.edu/tgn_browser/

Temporal

Name: temporal
Label: Temporal
Definition: Temporal characteristics of the intellectual content of the resource.

Encoding Schemes for Temporal:

DCMI Period

Name: Period
Label: DCMI Period
Definition: A specification of the limits of a time interval.
See also: http://purl.org/dc/documents/dcmi-period

W3C-DTF

Name: W3CDTF
Label: W3C-DTF
Definition: W3C Encoding rules for dates and times - a profile based on ISO 8601
See also: http://www.w3.org/TR/NOTE-datetime

Acknowledgements

This document represents the accumulated efforts of working group participants and working group chairs over a long period of time. In addition, the DCMI Usage Committee labored long and hard to integrate the efforts of these groups into a coherent recommendation. Thanks are due to these participants for the committment of their time and expertise in bringing this recommendation to fruition.

The following are the members of the DCMI Usage Committee: Leif Andresen, Tom Baker, David Bearman, Priscilla Caplan, Warwick Cathro, Eric Childress, Simon Cox, Makx Dekkers, Rebecca Guenther, Juha Hakala, Rachel Heery, Diane Hillmann, Renato Iannella, Erik Jul, Traugott Koch, John Kunze, Carl Lagoze, Sigfrid Lundberg, Jon Mason, Eric Miller, Andy Powell, Diann Rusch-Feja, Roland Schwaenzl, Shigeo Sugimoto, Stuart Sutton, Stuart Weibel.