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

Glossary:

This document follows the DCMI Abstract Model [DCAM] in its use of the following terminology:

term

A property (element), class, vocabulary encoding scheme, or syntax encoding scheme.

URI

A Uniform Resource Identifier [URI] or Internationalized Resource Identifier [IRI].

In addition, this document uses the following terminology:

DCMI term

Atermthat is declared and maintained by DCMI.

term URI

TheURIthat identifies aterm.

DCMI term URI

TheURIfor atermthat is declared and managed by DCMI.

term name

一个独特的令牌分配to aterm. For allDCMI terms,term nameis appended to aDCMI namespace URIto create theDCMI term URI.

term label

A human-readable label assigned to aterm.

DCMI namespace

A collection ofDCMI term URIswhere eachtermis assigned aURIthat starts with the same 'base URI'. The 'base URI' is known as theDCMI namespace URI. (Note that aDCMI namespaceis not the same as an 'XML namespace').

DCMI namespace URI

TheURIthat identifies aDCMI namespace.

DCMI recommendation

A specification, approved through DCMI's formal process, which may define one or moreDCMI terms.

DCMI term declaration

A representation of one or moreDCMI terms.

Term URIsare grouped intoDCMI namespacesin order to ease the assignment ofURIstotermsand to streamline their use in particular encoding syntaxes. Note that the grouping ofterm URIsintoDCMI namespacesis orthogonal to the grouping oftermsinto sets designed to meet other functional needs, e.g., as various types of vocabularies.

1. Introduction

Alltermsused in metadata descriptions that conform to the DCMI Abstract Model [DCAM] must be assigned a uniqueURI. For convenience, theterm URIsthat are assigned and managed by the DCMI are grouped into collections known asDCMI namespaces. This document describes howterm URIsare allocated by DCMI and the policies associated withDCMI namespaces.

2. DCMI Namespace URIs

TheDCMI namespace URIfor the collection of all DCMI properties, classes and encoding schemes (other than the properties in the Dublin Core™ Metadata Element Set, Version 1.1 [DCMES], the classes in the DCMI Type Vocabulary [DCMI-TYPE] and thetermsused in the DCMI Abstract Model) is:

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

TheDCMI namespace URIfor the collection ofclassesin the DCMI Type Vocabulary [DCMI-TYPE] is:

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

TheDCMI namespace URIfor the collection ofDCMI termsused in the DCMI Abstract Model is:

http://purl.org/dc/dcam/

TheDCMI namespace URIfor the collection of legacy properties that make up the Dublin Core™ Metadata Element Set, Version 1.1 [DCMES] is:

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

Therefore, the four currently approved DCMI namespace URIs are:

http://purl.org/dc/terms/	All DCMI properties, classes and encoding schemes (unless indicated below)
http://purl.org/dc/dcmitype/	Classes in the DCMI Type Vocabulary
http://purl.org/dc/dcam/	Terms used in the DCMI Abstract Model
http://purl.org/dc/elements/1.1/	The Dublin Core™ Metadata Element Set, Version 1.1 (original 15 elements)

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

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

AllDCMI namespace URIswill dereference to aDCMI term declarationfor all thetermswithterm URIswithin thatDCMI namespace. A machine-processableDCMI term declarationwill be made available.

Some exampleDCMI term URIsfollow:

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

is theDCMI term URIfor the Extentproperty.

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

is theDCMI term URIfor the Imageclassin the DCMI Type Vocabulary.

http://purl.org/dc/dcam/VocabularyEncodingScheme

is theDCMI term URIforVocabulary Encoding Schemeclass in the DCMI Abstract Model, and

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

is theDCMI term URIfor the Titlepropertyin the Dublin Core™ Metadata Element Set, Version 1.1.

每一个DCMI termcan be so identified.

AllDCMI term URIswill dereference to aDCMI term declarationfor the identifiedterm. A machine-processableDCMI term declarationwill be made available.

3. Policy concerning classes of changes to DCMI terms

Changes toDCMI termsorterm declarationswill occur from time to time for a variety of reasons. Such changes have varying implications forDCMI term URIsandDCMI namespaces. The following classes of changes are identified along with examples and associated implications.

In all cases, any changes toDCMI termsorterm declarationswill result in an update to the versioning information carried in theDCMI recommendationand/orDCMI term declaration与thatterm.

A. Minor editorial errata

Errors of spelling, punctuation, or other clerical mistakes discovered inDCMI recommendationsand/orDCMI term declarationswill 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 thoseDCMI term declarations.

Correction of minor editorial errata will result in no changes toDCMI term URIs.

B. Substantive editorial errata

Errors of substance discovered inDCMI recommendationsand/orDCMI term declarationswill 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 theDCMI namespaceinfrastructure.

Correction of substantive editorial errata will result in no changes inDCMI term URIs.

C. Semantic changes in DCMI terms

Changes of definitions withinDCMI recommendationsand/orDCMI term declarationswill be reflected in the affectedDCMI recommendationand/orDCMI term declaration. If, in the judgment of the DCMI Directorate, such changes of meaning are likely to have substantial impact on either machine processing ofDCMI termsor the functional semantics of theterms,n these changes will be reflected in a change of URI for theDCMI termortermsin question. The URIs for any newDCMI namespacesresulting from such changes will conform to theDCMI namespace URIpattern defined above.

d .的现有DCMI术语声明DCMI namespaces

NewDCMI term URIswill occasionally be added to existingDCMI namespaces. Addition ofDCMI term URIsto existingDCMI namespaceswill not trigger changes inDCMI namespace URIs.

4. Persistence Policy

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 ofDCMI term URIsandDCMI namespace URIsis critical to interoperability over time. Thus, the wide promulgation of this set ofURIsdictates that they be maintained to support legacy applications that have adopted them.

5. Justification

Two significant suggestions were made during the development of this policy in 2001. Firstly, it was suggested thatDCMI namespace URIsindicate the category ofDCMI terms与that namespace. For example, it was proposed that differentDCMI namespacesmight be used to partition DCMI properties from DCMI encoding schemes, or to indicate that a particulartermwas originally defined by a particular community or within a particular domain. Secondly, that allDCMI namespace URIscarry 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 ofDCMI termsis not necessarily persistent. For example,termsdefined initially by the education community might subsequently become useful to other communities. Associating particular URIs with particular categories oftermswas not felt to be helpful to the long-term stability ofDCMI namespacesor the URIs ofDCMI termswithin those namespaces.

On the second issue it was again considered that embedding versioning information within theDCMI namespace URIwas unlikely to be helpful to the long-term stability ofDCMI namespace URIsorDCMI term URIswithin thoseDCMI namespaces. Rather, it was felt that versioning information should be carried within theDCMI recommendationsand/orDCMI term declarations与DCMI namespacesandterms.

References

[DCAM]
Powell, Andy, Mikael Nilsson, Ambjörn Naeve, Pete Johnston and Thomas Baker. DCMI Abstract Model. DCMI Proposed Recommendation. February 2007.
<//www.voudr.com/specifications/dublin-core/abstract-model/2007-02-05/>

[DCMES]
Dublin Core™ Metadata Element Set, Version 1.1: Reference Description
<//www.voudr.com/specifications/dublin-core/dces/>

[DCMI-TYPE]
DCMI Type Vocabulary, DCMI Recommendation, 11 July 2000
<//www.voudr.com/specifications/dublin-core/dcmi-type-vocabulary/>

[DCMI-USAGE]
DCMI Usage Board
<//www.voudr.com/usage/>

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

[IRI]
Duerst, M., M. Suignard. RFC 3987: Internationalized Resource Identifiers (IRIs). Internet Engineering Task Force (IETF). January 2005.
<http://www.ietf.org/rfc/rfc3987.txt>

[URI]
Berners-Lee, T., R. Fielding, L. Masinter. RFC 3986: Uniform Resource Identifier (URI): Generic Syntax. Internet Engineering Task Force (IETF). January 2005.
<http://www.ietf.org/rfc/rfc3986.txt>