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

A term that is declared and maintained by DCMI.

term URI

The URI that identifies a term.

DCMI term URI

The URI for a term that is declared and managed by DCMI.

term name

A unique token assigned to a term. For all DCMI terms, the term name is appended to a DCMI namespace URI to create the DCMI term URI.

term label

A human-readable label assigned to a term.

DCMI namespace

A collection of DCMI term URIs where each term is assigned a URI that starts with the same 'base URI'. The 'base URI' is known as the DCMI namespace URI. (Note that a DCMI namespace is not the same as an 'XML namespace').

DCMI namespace URI

The URI that identifies a DCMI namespace.

DCMI recommendation

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

DCMI term declaration

A representation of one or more DCMI terms.

Term URIs are grouped into DCMI namespaces in order to ease the assignment of URIs to terms and to streamline their use in particular encoding syntaxes. Note that the grouping of term URIs into DCMI namespaces is orthogonal to the grouping of terms into sets designed to meet other functional needs, e.g., as various types of vocabularies.

1. Introduction

All terms used in metadata descriptions that conform to the DCMI Abstract Model [DCAM] must be assigned a unique URI. For convenience, the term URIs that are assigned and managed by the DCMI are grouped into collections known as DCMI namespaces. This document describes how term URIs are allocated by DCMI and the policies associated with DCMI namespaces.

2. DCMI Namespace URIs

The DCMI namespace URI for 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 the terms used in the DCMI Abstract Model) is:

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

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

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

The DCMI namespace URI for the collection of DCMI terms used in the DCMI Abstract Model is:

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

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

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

All DCMI namespace URIs will dereference to a DCMI term declaration for all the terms with term URIs within that DCMI namespace. A machine-processable DCMI term declaration will be made available.

Some example DCMI term URIs follow:

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

is the DCMI term URI for the Extent property.

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

is the DCMI term URI for the Image class in the DCMI Type Vocabulary.

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

is the DCMI term URI for Vocabulary Encoding Scheme class in the DCMI Abstract Model, and

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

is the DCMI term URI for the Title property in the Dublin Core™ Metadata Element Set, Version 1.1.

Each DCMI term can be so identified.

All DCMI term URIs will dereference to a DCMI term declaration for the identified term. A machine-processable DCMI term declaration will be made available.

3. 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 term URIs and DCMI namespaces. The following classes of changes are identified along with examples and associated implications.

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 to DCMI term 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 term 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 URI 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 URI pattern defined above.

D. Addition of DCMI term declarations to existing DCMI namespaces

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

5. Justification

Two significant suggestions were made during the development of this policy in 2001. Firstly, it was suggested that DCMI namespace URIs indicate the category of DCMI terms associated with that namespace. For example, it was proposed that different DCMI namespaces might be used to partition DCMI properties from DCMI encoding schemes, 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 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 is 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 DCMI namespace URI was unlikely to be helpful to the long-term stability of DCMI namespace URIs or DCMI term URIs within those DCMI 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.

References

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

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

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

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