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Namespace Policy for the Dublin Core™ Metadata Initiative (DCMI)

Namespace Policy for the Dublin Core™ Metadata Initiative (DCMI) (SUPERSEDED, SEE CURRENT VERSION)

Editor: Andy Powell
Editor: Harry Wagner
Contributor: Stuart Weibel
Contributor: Tom Baker
Contributor: Tod Matola
Contributor: Eric Miller
Date Issued: 2001-10-26
Identifier: http://dublincore.org/specifications/dublin-core/dcmi-namespace/2001-10-26/
Replaces: http://dublincore.org/specifications/dublin-core/dcmi-namespace/2001-09-17/
Is Replaced By: http://dublincore.org/specifications/dublin-core/dcmi-namespace/2007-07-02/
Latest version: http://dublincore.org/specifications/dublin-core/dcmi-namespace/
Status of document: This is a DCMI Recommendation
Description of document:

An XML namespace [XML-NAMES] is a collection of names, identified by a URI reference [RFC2396], that are used in XML documents as element types and attribute names. The use of XML namespaces to uniquely identify metadata terms allows those terms to be unambiguously used across applications, promoting the possibility of shared semantics. DCMI adopts this mechanism for the identification of all DCMI terms.

This document specifies the conventions used for identifying current and future DCMI namespaces. All DCMI recommendations that make use of namespaces will conform to this recommendation.

Glossary:

The following are defined terms in this document:

  • DCMI term
    A DCMI term is a DCMI element, a DCMI qualifier or term from a DCMI-maintained controlled vocabulary. Each DCMI term is defined in a DCMI recommendation and is identified by a Uniform Resource Identifier (URI) within a DCMI namespace.
  • DCMI namespace
    A DCMI namespace is a collection of DCMI terms. Each DCMI namespace is identified by a URI.
  • DCMI recommendation
    A DCMI recommendation is a human-readable document that may define one or more DCMI terms.
  • DCMI term declaration
    A DCMI term declaration is the machine-processable representation of one or more DCMI terms, expressed in a schema language.

I. Introduction

An XML namespace [XML-NAMES] is a collection of names, identified by a URI reference [RFC2396], that are used in XML documents as element types and attribute names. The use of XML namespaces to uniquely identify metadata terms allows those terms to be unambiguously used across applications, promoting the possibility of shared semantics. DCMI adopts this mechanism for the identification of all DCMI terms.

This document specifies the conventions used for identifying current and future DCMI namespaces. All DCMI recommendations that make use of namespaces will conform to this recommendation.

II. Namespace URIs used by the DCMI

The URI of the namespace for all DCMI elements that comprise the Dublin Core™ Metadata Element Set, Version 1.1 [DCMES] is:

http://purl.org/dc/elements/1.1/

The URI of the namespace for all DCMI elements and DCMI qualifiers (other than those elements defined in the Dublin Core™ Metadata Element Set, Version 1.1 above) is:

http://purl.org/dc/terms/

The URI of the namespace for DCMI terms defined in the DCMI Type Vocabulary [DCMI-TYPE] is:

http://purl.org/dc/dcmitype/

Therefore, the three currently approved DCMI namespace URIs are:

http://purl.org/dc/elements/1.1/ Dublin Core™ Metadata Element Set, Version 1.1 (15 elements)
http://purl.org/dc/terms/ DCMI elements and DCMI qualifiers (other than those elements defined in the Dublin Core™ Metadata Element Set, Version 1.1 above)
http://purl.org/dc/dcmitype/ DCMI terms in the DCMI Type Vocabulary (a DCMI controlled vocabulary)

All DCMI namespace URIs will resolve to a machine-processable DCMI term declaration for all the terms within that namespace.

The URI for each DCMI term is constructed by appending the term name to the namespace URI for that term. For example:

http://purl.org/dc/elements/1.1/title

is the URI for the Title element in the Dublin Core™ Metadata Element Set, Version 1.1,

http://purl.org/dc/terms/extent

is the URI for the Extent qualifier in the Dublin Core™ Qualifiers recommendation [DCQ] and

http://purl.org/dc/dcmitype/Image

is the URI for the Image term in the DCMI Type Vocabulary. Each DCMI term can be so identified.

All future DCMI namespace URIs (additional DCMI controlled vocabularies for example) will conform to this pattern:

http://purl.org/dc/namespace_label/

III. Policy concerning classes of changes to DCMI terms

Changes to DCMI terms or term declarations will occur from time to time for a variety of reasons. Such changes have varying implications for DCMI namespaces. The following classes of changes are identified along with examples and associated implications for namespaces.

In all cases, any changes to DCMI terms or term declarations will result in an update to the versioning information carried in the DCMI recommendation and/or DCMI term declaration associated with that term.

A. Minor editorial errata

Errors of spelling, punctuation, or other clerical mistakes discovered in DCMI recommendations and/or DCMI term declarations will be corrected without a comment period, following notification to the DCMI Usage Board [DCMI-USAGE], as long as, in the judgment of the DCMI Directorate, there are no implications for negative impact on users or applications that rely on those DCMI term declarations.

Correction of minor editorial errata will result in no changes in DCMI namespace URIs.

B. Substantive editorial errata

Errors of substance discovered in DCMI recommendations and/or DCMI term declarations will trigger public notification of the correction to the DC-General mailing list [DC-GENERAL]. Errors that, in the judgment of the DCMI Directorate, compromise the immediate usefulness or accuracy of DCMI metadata systems will be corrected immediately (for example, an incorrect URL to a resource external to DCMI). Others will be corrected following a 14-day public comment period to assure that changes do not adversely effect systems or applications which rely on the DCMI namespace infrastructure.

Correction of substantive editorial errata will result in no changes in DCMI namespace URIs.

C. Semantic changes in DCMI terms

Changes of definitions within DCMI recommendations and/or DCMI term declarations will be reflected in the affected DCMI recommendation and/or DCMI term declaration. If, in the judgment of the DCMI Directorate, such changes of meaning are likely to have substantial impact on either machine processing of DCMI terms or the functional semantics of the terms, then these changes will be reflected in a change of name or namespace for the DCMI term or terms in question. The URIs for any new DCMI namespaces resulting from such changes will conform to the DCMI namespace pattern defined above.

D. Addition of DCMI term declarations to existing DCMI namespaces

New terms will occasionally be added to existing DCMI namespaces. Addition of DCMI terms to existing namespaces will not trigger changes in namespace URIs.

IV. Persistence Policy

The DCMI recognizes that people and applications depend on the persistence of formal documents and machine processable schemas that have been made publicly available. In particular, the stability of namespace URIs for metadata terms is critical to interoperability over time. Thus, the wide promulgation of this set of URIs dictates that they be maintained to support legacy applications that have adopted them.

V. Justification

Two significant issues were raised during the development of this policy. Firstly, that DCMI namespace URIs should indicate the category of DCMI terms within that namespace. For example, it was proposed that different DCMI namespaces might be used to partition DCMI elements from DCMI qualifiers, or to indicate that a particular term was originally defined by a particular community or within a particular domain. Secondly, that all DCMI namespace URIs should carry versioning information (for example a date stamp) that would be updated as terms within the namespace change.

On the first issue it was considered that the category of DCMI terms was not necessarily persistent. For example, terms defined initially by the education community might subsequently become useful to other communities. Associating particular URIs with particular categories of terms was not felt to be helpful to the long-term stability of DCMI namespaces or the URIs of DCMI terms within those namespaces.

On the second issue it was again considered that embedding versioning information within the namespace URI was unlikely to be helpful to the long-term stability of DCMI namespaces or the URIs of DCMI terms within those namespaces. Rather, it was felt that versioning information should be carried within the DCMI recommendations and/or DCMI term declarations associated with DCMI namespaces and terms.

Finally it should be noted that, although the 15 elements currently within the http://purl.org/dc/elements/1.1/ namespace could have been redefined within the http://purl.org/dc/terms/ namespace, it was considered that the widespread existing usage of the former namespace URI mitigated against any change. Furthermore, the existing use of the purl.org domain for that namespace URI prompted its use for all DCMI namespace URIs.

References

[XML-NAMES]
Namespaces in XML, W3C Recommendation, 14 January 1999
http://www.w3.org/TR/REC-xml-names

[RFC2396]
IETF (Internet Engineering Task Force) RFC 2396: Uniform Resource Identifiers (URI): Generic Syntax, eds. T. Berners-Lee, R. Fielding, L. Masinter. August 1998.

[DCMES]
Dublin Core™ Metadata Element Set, Version 1.1: Reference Description
http://dublincore.org/specifications/dublin-core/dces/1999-07-02/

[DCMI-TYPE]
DCMI Type Vocabulary, DCMI Recommendation, 11 July 2000
http://dublincore.org/specifications/dublin-core/dcmi-type-vocabulary/

[DCQ]
Dublin Core™ Qualifiers
http://dublincore.org/specifications/dublin-core/dcmes-qualifiers/

[DCMI-USAGE]
DCMI Usage Board
http://dublincore.org/usage/

[DC-GENERAL]
DC-General mailing list
http://www.jiscmail.ac.uk/lists/dc-general.html