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DCMI Abstract Model

Creator: Andy Powell
Eduserv Foundation, UK
Creator: Mikael Nilsson
KMR Group, CID, NADA, KTH (Royal Institute of Technology), Sweden
Creator: Ambjörn Naeve
KMR Group, CID, NADA, KTH (Royal Institute of Technology), Sweden
Creator: Pete Johnston
Eduserv Foundation, UK
Creator: Thomas Baker
DCMI
Date Issued: 2007-02-05
Identifier: http://dublincore.org/specifications/dublin-core/abstract-model/2007-02-05/
Replaces: http://dublincore.org/specifications/dublin-core/abstract-model/2005-03-07/
Is Replaced By: Not applicable
Latest Version: http://dublincore.org/specifications/dublin-core/abstract-model/
Status of Document: This is a DCMIProposed Recommendation
Description of Document: This document describes an abstract model for Dublin Core™ metadata.

Table of contents

  1. Introduction
  2. DCMI Abstract Model
  3. Descriptions, description sets and records
  4. Values
  5. DCMI Abstract Model semantics
  6. Encoding guidelines
  7. Terminology
    Appendix A - Relationship to legacy DCMI Grammatical Principles
    References
    Acknowledgements

1. Introduction

This document specifies an abstract model for Dublin Core™ metadata. The primary purpose of this document is to specify the components and constructs used in Dublin Core™ metadata. It defines the nature of the components used and describes how those components are combined to create information structures. It provides a reference model which is independent of any particular encoding syntax. Such a reference model allows us to gain a better understanding of the kinds of descriptions that we are trying to encode and facilitates the development of better mappings and cross-syntax translations.

本文主要是针对开发人员elopers of software applications that support Dublin Core™ metadata, people involved in developing new syntax encoding guidelines for Dublin Core™ metadata and people developing metadata application profiles based on DCMI vocabularies or on other compatible vocabularies.

The DCMI Abstract Model builds on work undertaken by the World Wide Web Consortium (W3C) on the Resource Description Framework (RDF) [RDF, RDFS]. The use of concepts from RDF is summarized below in Section 5, on DCMI Abstract Model semantics.

The DCMI Abstract Model is represented here using UML class diagrams [UML]. Readers that are not familiar with UML class diagrams should note that lines ending in a block-arrow should be read as 'is' or 'is a' (for example, "avalueis aresource") and that lines starting with a block-diamond should be read as 'contains a' or 'has a' (for example, "astatementcontains aproperty URI"). Other relationships are labeled appropriately. Note that the UML modeling used here shows the abstract model but is not intended to form a suitable basis for the development of software applications. In this document, words and phrases in italics are defined in Section 7, Terminology.

2. DCMI Abstract Model

The abstract model of theresourcesdescribed bydescriptionsis as follows:

  • Eachdescribed resourcemay be described using one or moreproperty-value pairs．

  • Eachproperty-value pairis made up of onepropertyand onevalue．

  • Eachvalueis aresource- the physical or conceptual entity that is associated with aproperty当一个property-value pairis used to describe aresource．

Figure 1 - the DCMI resource model**Figure 1 - the DCMI resource model**

The abstract model of DC metadatadescriptionsis as follows:

  • Adescription setis a set of one or moredescriptions, each of which describes a singleresource．

  • Adescriptionis made up of one or morestatements(about one, and only one,described resource) and zero or oneresource URI(aURIthat identifies thedescribed resource).

  • Eachstatementinstantiates aproperty-value pairand is made up of aproperty URI(aURIthat identifies aproperty), zero or onevalue URI(aURIthat identifies thevalueassociated with theproperty), zero or onevocabulary encoding scheme URI(aURIthat identifies thevocabulary encoding schemeof which thevalueis a member), and zero or morevalue representations．

  • Thevalue representationmay take the form of avalue stringor arich representation．

  • Eachvalue stringis a string which represents theresource．Value stringsare intended to be human-readable.

  • Eachvalue stringmay have either an associatedsyntax encoding scheme URIthat identifies asyntax encoding schemeor an associatedvalue string languagethat is an ISO language tag (for example en-GB) but not both.

  • Eachrich representationis a sequence of octets that represents thevalue(aresource) - for example, some marked-up text, an image, a video, some audio, or some combination thereof.

  • Eachrich representationmust have an associatedmedia type(a MIME Media Type).

Figure 2 - the DCMI description model**Figure 2 - the DCMI description model**

The abstract model of the vocabularies used in DC metadatadescriptionsis as follows:

  • Eachpropertymay be related to one or moreclassesby ahas domainrelationship. Where it is stated that apropertyhas such a relationship with aclassand adescribed resourceis related to avalueby thatproperty, it follows that thedescribed resourceis an instance of thatclass．

  • Eachpropertymay be related to one or moreclassesby ahas rangerelationship. Where it is stated that apropertyhas such a relationship with aclassand adescribed resourceis related to avalueby thatproperty, it follows that thevalueis an instance of thatclass．

  • Eachresourcemay be aninstance ofone or moreclasses．

  • Eachresourcemay be amember ofone or morevocabulary encoding schemes．

  • Eachclassmay be related to one or more otherclassesby asub-class ofrelationship (where the twoclassesare defined such that allresourcesthat are instances of the sub-class are also instances of the relatedclass).

  • Eachpropertymay be related to one or more otherpropertiesby asub-property ofrelationship. Where it is stated that such a relationship exists, the twopropertiesare defined such that whenever aresourceis related to avalueby the sub-property, it follows that theresourceis also related to that samevalueby theproperty．

  • Eachsyntax encoding schemeis aclass(of strings).

  • Avocabularyis a set of one or moreterms．Eachtermis a member of one or morevocabularies．

Figure 3 - the DCMI vocabulary model**Figure 3 - the DCMI vocabulary model**

A number of things about the model are worth noting:

  • Eachvaluemay be thedescribed resourcein a separatedescriptionwithin the same description set - for example, a separatedescriptionmay provide metadata about the person that is the creator of thedescribed resource．

  • The description model does not provide an explicit mechanism for indicating theclassesof thedescribed resourceor theclassesof any givenvalue．Classesof thedescribed resourcecan either be indicated explicitly using one or morestatementsin thedescriptionor be inferred from thedomainsof thepropertiesused in thedescription．Classesof any givenvaluecan either be indicated explicitly using one or morestatementsin a separatedescriptionabout thatvalueor be inferred from therangeof theproperty．

3. Descriptions, description sets and records

The abstract model presented above indicates that each DC metadatadescriptiondescribes one, and only one,described resource．This is commonly referred to as the one-to-one principle.

However, real-world metadata applications tend to be based on loosely grouped sets ofdescriptions(where thedescribed resourcesare typically related in some way), known here asdescription sets．For example, adescription setmight comprisedescriptionsof both a painting and the artist. Furthermore, it is often the case that adescription setwill also contain adescriptionabout thedescription setitself (sometimes referred to as 'admin metadata' or 'meta-metadata').

Description setsare instantiated, for the purposes of exchange between software applications, in the form of metadatarecords, according to one of the DCMI encoding guidelines (for example, XHTML meta tags, XML and RDF/XML) [DCMI-ENCODINGS].

4. Values

A DC metadatavalueis the physical or conceptual entity that is associated with aproperty当一个property-value pairis used to describe aresource．For example, avalueassociated with the Dublin Core™ Creatorpropertyis a person, organization or service - a physical entity. Avalueassociated with the Dublin Core™ Datepropertyis a point (or range) in time - a conceptual entity. Avalueassociated with the Dublin Core™ Coveragepropertyis a geographic region or country - a physical entity. Avalueassociated with the Dublin Core™ Subjectpropertyis a concept (a conceptual entity) or a physical object or person (a physical entity). Each of these entities is aresource．

Thevaluemay be identified using avalue URI．Thevaluemay be represented by one or morevalue stringsand/orrich representations．Thevaluemay described by a separatedescription．In each case, thevalueis aresource．

5. DCMI Abstract Model semantics

Some of the concepts in the DCMI Abstract Model are taken from the Resource Description Framework (RDF) and RDF Schema (RDFS) as follows:

DCMI Abstract Model RDF/RDFS
resource Class:http://www.w3.org/2000/01/rdf-schema#Resource
propertyorelement Class:http://www.w3.org/1999/02/22-rdf-syntax-ns#Property
class Class:http://www.w3.org/2000/01/rdf-schema#Class
syntax encoding scheme Class:http://www.w3.org/2000/01/rdf-schema#Datatype
has domainrelationship Property:http://www.w3.org/2000/01/rdf-schema#domain
has rangerelationship Property:http://www.w3.org/2000/01/rdf-schema#range
sub-property ofrelationship Property:http://www.w3.org/2000/01/rdf-schema#subPropertyOf
sub-class ofrelationship Property:http://www.w3.org/2000/01/rdf-schema#subClassOf

Table 1 - DCMI Abstract Model semantics

6. Encoding guidelines

Particular encoding guidelines (HTML meta tags, XML, RDF/XML, etc.) [DCMI-ENCODINGS] do not need to encode all aspects of the abstract model described above. However, they should refer to the DCMI Abstract Model and indicate which parts of the model are encoded and which are not.

Encoding guidelines should indicate how avaluecan be treated as adescribed resourcein a separatedescriptionin those cases where there is novalue URI．

7. Terminology

This document uses the following terms:

class(http://www.w3.org/2000/01/rdf-schema#Class)
A group containing members that have attributes, behaviours, relationships or semantics in common; a kind of category.
described resource
Aresourcethat is described by adescription．
described resource URI
AURIthat identifies thedescribed resource．
description
One or morestatementsabout one, and only one,described resource．
description set
A set of one or moredescriptions．
element(http://www.w3.org/1999/02/22-rdf-syntax-ns#Property)
A synonym forproperty．It should be noted that the word element is also commonly used to refer to a structural markup component within an XML document.
has domain(http://www.w3.org/2000/01/rdf-schema#domain)
A relationship between apropertyand aclasswhich indicates that if adescribed resourceis related to avalueby theproperty, then it follows that thedescribed resourceis an instance of thatclass．
has range(http://www.w3.org/2000/01/rdf-schema#range)
A relationship between apropertyand aclasswhich indicates that if adescribed resourceis related to avalueby theproperty, then it follows that thevalueis an instance of thatclass．
instance of
A relationship between aresourceand aclasswhich indicates aclassof which theresourceis an instance.
media type
A MIME Media Type (as defined by RFC 2045 [MIME-1] and RFC 2046 [MIME-2].
member of(Proposed URI:http://purl.org/dc/dcam/memberOf)
A relationship between aresourceand avocabulary encoding schemewhich indicates that theresourceis a member of a set.
property(http://www.w3.org/1999/02/22-rdf-syntax-ns#Property)
A specific aspect, characteristic, attribute, or relation used to describeresources．
property URI
AURIthat identifies a singleproperty．
property/value pair
The combination of apropertyand avalue, used to describe aresource．
record
An instantiation of adescription set, created according to one of the DCMI encoding guidelines (for example, XHTML meta tags, XML and RDF/XML).
resource(http://www.w3.org/2000/01/rdf-schema#Resource)
Anything that might be identified. Familiar examples include an electronic document, an image, a service (for example, "today's weather report for Los Angeles"), and a collection of otherresources．Not allresourcesare network "retrievable"; for example, human beings, corporations, concepts and bound books in a library can also be consideredresources．
rich representation
A sequence of octets that represents thevalue-- for example, some marked-up text, an image, a video, some audio, or some combination thereof.
statement
An instantiation of aproperty-value pairmade up of aproperty URI(aURIthat identifies aproperty), zero or onevalue URI(aURIthat identifies thevalueassociated with theproperty), zero or onevocabulary encoding scheme URI(aURIthat identifies thevocabulary encoding schemeof which thevalueis a member), and zero or morevalue representationsof thevalue．
sub-class of(http://www.w3.org/2000/01/rdf-schema#subClassOf)
A relationship between twoclasseswhich indicates that the twoclassesare defined such that allresourcesthat are instances of the sub-classare also instances of the relatedclass).
sub-property of(http://www.w3.org/2000/01/rdf-schema#SubPropertyOf)
A relationship between twopropertieswhich indicates that the twopropertiesare defined such that whenever aresourceis related to avalueby the sub-property, it follows that theresourceis also related to that samevalueby theproperty．
syntax encoding scheme(http://www.w3.org/2000/01/rdf-schema#Datatype)
A set of strings and an associated set of rules that describe a mapping between that set of strings and a set ofresources．映射规则可以定义字符串的年代tructured (for example DCMI Box) or they may simply enumerate all the strings and the corresponding resources (for example ISO 3166).
syntax encoding scheme URI
AURIthat identifies asyntax encoding scheme．
term
Aproperty(element),class,vocabulary encoding scheme, orsyntax encoding scheme．
URI
A Uniform Resource Identifier [URI] or Internationalized Resource Identifier [IRI].
value
The physical or conceptual entity (aresource) that is associated with aproperty当一个property-value pairis used to describe aresource．
value URI
AURIthat identifies thevalue．
value representation
A surrogate for (i.e. a representation of) thevalue．
value string
A string, optionally associated with either asyntax encoding scheme URIor avalue string language, which represents thevalue．
value string language
一个ISO语言标签显示的语言thevalue string．
vocabulary
A set of one or moreterms．
vocabulary encoding scheme(Proposed URI:http://purl.org/dc/dcam/VocabularyEncodingScheme)
An enumerated set ofresources．
vocabulary encoding scheme URI
AURIthat identifies avocabulary encoding scheme．

Appendix A - Relationship to legacy DCMI Grammatical Principles

™都柏林核心元数据的底层模型evolved since first formalisms were proposed in the late 1990s. The following table presents rough terminological equivalences between earlier versions of DCMIgrammatical principles[DCMI-GRAM-PRIN] and the current DCMI Abstract Model.

DCMI Grammatical Principles DCMI Abstract Model
vocabulary term resource
element propertyorelement
element refinement propertywithsub-property ofrelation
encoding scheme syntax encoding schemeorvocabulary encoding scheme
syntax encoding scheme syntax encoding scheme
qualifier propertywithsub-property ofrelation,syntax encoding scheme, orvocabulary encoding scheme
vocabulary encoding scheme vocabulary encoding scheme

Table 2 - DCMI Grammatical Principles and DCMI Abstract Model

References

[DCMI]
Dublin Core™ Metadata Initiative
<http://dublincore.org/>

[DCMI-GRAM-PRIN]
DCMI Usage Board. DCMI Grammatical Principles. November 2003.
<http://dublincore.org/specifications/dublin-core/grammatical-principles/>

[DCMI-ENCODINGS]
DCMI Encoding Guidelines
<http://dublincore.org/schemas/>

[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>

[MIME-1]
Freed, N. and N. Borenstein. RFC 2045: Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies. Internet Engineering Task Force (IETF). November 1996.
<http://www.ietf.org/rfc/rfc2045.txt>

[MIME-2]
Freed, N. and N. Borenstein. RFC 2045: Multipurpose Internet Mail Extensions (MIME) Part Two: Media Types. Internet Engineering Task Force (IETF). November 1996.
<http://www.ietf.org/rfc/rfc2046.txt>

[RDF]
Klyne, Graham and Jeremy Carroll, editors. Resource Description Framework: Concepts and Abstract Syntax. W3C Recommendation. 10 February 2004.
<http://www.w3.org/TR/rdf-concepts/>

[RDFS]
Brickley, Dan and R.V. Guha, editors. RDF Vocabulary Description Language 1.0: RDF Schema. W3C Recommendation. 10 February 2004.
<http://www.w3.org/TR/rdf-schema/>

[UML]
Booch, Grady, James Rumbaugh and Ivar Jacobson. The Unified Modeling Language User Guide. Addison-Wesley, 1998.

[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>

Acknowledgements

Thanks to Dan Brickley, Rachel Heery, Alistair Miles, Sarah Pulis, the members of the DC Usage Board and the members of the DCMI Architecture Community for their comments on previous versions of this document.