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Guidelines for Encoding Bibliographic Citation Information in Dublin Core Metadata

Creator: Ann Apps, MIMAS, The University of Manchester, UK. ann.apps@manchester.ac.uk
Contributor Dublin Core Metadata Initiative Citation Working Group
Date Issued: 2005-06-13
Identifier: http://dublincore.org/documents/2005/06/13/dc-citation-guidelines/
Replaces: http://dublincore.org/documents/2005/04/15/dc-citation-guidelines/
Is Replaced By: Not applicable
Latest Version: http://dublincore.org/documents/dc-citation-guidelines/
Status of Document: This is a DCMI Recommendation.
Description This document provides guidelines for capturing bibliographic citation information within a Dublin Core description. It focuses on bibliographic citations for journal articles, but it also considers other genre. It deals primarily with bibliographic citations for a resource within its own metadata, but some guidelines for describing references to other resources are also indicated. Some other issues that arise when describing a bibliographic resource using Dublin Core metadata are also discussed.

1 Introduction and Scope

This document provides guidelines for capturing bibliographic citation information within a Dublin Core description. It focuses primarily on:

In addition to a need to describe bibliographic citation information for discovery and for reading by humans after retrieval of a record, some applications have a requirement to encode this information in a format suitable for machine reading. These guidelines suggest the use of descriptions taken from the OpenURL Framework standard (Z39.88-2004) [1], rather than inventing an alternative DCMI syntax.

Many implementations have needed a way to describe journal articles and, because of the lack of any guidelines, have invented many ad hoc solutions, which solve the problem locally but discourage interoperability. These guidelines provide a recommended and thus interoperable way to encode bibliographic citation information within a Dublin Core description.

It is expected that these guidelines will be useful when the intention is to use Dublin Core metadata to describe bibliographic items for resource discovery or for simple, interoperable resource description. These guidelines do not aim to provide a solution for more complex metadata description requirements, and they do not seek to replace metadata schemes more suitable in such cases. For more detailed ways to describe bibliographic items in XML, it is suggested that alternatives schemes, for example PRISM [2], MODS [3], or NLM Data [4], may be more appropriate.

This document does not provide detailed guidelines for the XML encoding of bibliographic citation information in Dublin Core. Guidelines for XML encoding will be published in a separate, future document.

In the various tables of data below a disctinction is made between property values that are simple strings, known as 'value strings', and those that should be interpreted as URIs, known as 'value URIs'. Where appropriate a vocabulary encoding scheme is indicated for a value string.

The following abbreviations are used for Dublin Core namespaces within this document:

Abbreviation Namespace
dc: http://purl.org/dc/elements/1.1/
dcterms: http://purl.org/dc/terms/

These guidelines are the outcome of discussions over several years by the DCMI Citation Working Group [5]. They supersede and deprecate any previous proposed recommendations by the group other than those that have been endorsed by the DCMI Usage Board. Before the introduction of the Dublin Core term 'bibliographicCitation' it was not obvious how to describe fully a journal article using Dublin Core metadata. There was no suitable Dublin Core property to capture the journal title, as distinct from the article title, or the volume, issue and page details, other than as part of a general description. Various suggested solutions were proposed, the most attractive one being to describe the journal and issue information as an 'isPartOf' relation, but this would not include the page details, those being pertinent to the article itself.

2 Bibliographic Citations in Qualified Dublin Core

2.1 Citation Information within a Described Resource

Recommendation 1. Use dcterms:bibliographicCitation to capture the bibliographic citation information for a resource.

The recommended property to describe the bibliographic citation information for a resource within its own metadata is dcterms:bibliographicCitation. This is an element refinement of dc:identifier, defined in the 'dcterms' namespace. The value of this property would hold details of the bibliographic item that contains the resource along with the position of the resource within it. Thus for a journal article it could capture the journal title, volume and issue numbers, pagination and publication date, or for a book chapter the book details and pagination. Other details of the resource, such as its title and creators, will be described using the usual Dublin Core properties. Optionally, but redundantly, these details may be included in the citation as well. The ISSN of a journal or the ISBN of a book may be captured as a value URI within a dcterms:isPartOf relation property. Examples 1 and 2 show Dublin Core metadata descriptions for a journal article and a conference paper. These are given in tabular form, rather than any specific syntax, but would be suitable for use within any recommended Dublin Core syntax.


Example 1. A Dublin Core Description of a Journal Article

Property Encoding Scheme URI Value String Value URI
dc:title   Studying E-Journal User Behavior Using Log Files  
dc:creator   Yu, L  
dc:creator   Apps, A  
dc:subject http://purl.org/dc/terms/DDC 020  
dc:subject http://purl.org/dc/terms/LCC Z671  
dc:publisher   Elsevier  
dc:type http://purl.org/dc/terms/DCMIType Text  
dcterms:issued http://purl.org/dc/terms/W3CDTF 2000  
dcterms:isPartOf     urn:ISSN:0740-8188
dcterms:bibliographicCitation   Library and Information Science Research 22(3), 311-338. (2000)  

Example 2. A Dublin Core Description of a Conference Paper

Property Encoding Scheme URI Value String Value URI
dc:title   Exposing Cross-Domain Resources for Researchers and Learners  
dc:creator   Apps, A  
dc:creator   MacIntyre, R  
dc:subject   Dublin Core  
dc:subject   metadata  
dc:subject   e communities  
dc:publisher   Firenze University Press  
dc:type http://purl.org/dc/terms/DCMIType Text  
dcterms:issued http://purl.org/dc/terms/W3CDTF 2002  
dcterms:isPartOf     urn:ISBN:8884530431
dcterms:bibliographicCitation   Proceedings of the International Conference on Dublin Core and metadata for e-communities, 2002; DC-2002: Metadata for e-Communities: Supporting Diversity and Convergence, Florence, Italy, 13-17 October 2002, pp 71-80  

2.2 Text Citations

Recommendation 2. Always provide a plain text citation

For general resource discovery and human readability the value of a bibliographicCitation property should be given in plain text. Even when a machine-parsable citation is provided, it is recommended that the citation be repeated as a corresponding plain text citation.

Plain text citations may be according to a recognised citation style. Several styles were reviewed by the DCMI Citation Working Group, and are listed on a Citation Styles [6] page, but there is no particular recommendation for choice of style. The style used can be indicated as an encoding scheme if it has a URI. Otherwise, there is no DCMI endorsed encoding scheme to indicate a citation style.

Recommendation 3. A text bibliographic citation should contain sufficient detail to identify the resource.

A text bibliographic citation should contain sufficient detail to identify the resource by that citation. dcterms:bibliographicCitation is an element refinement of dc:identifier, recognising that a bibliographic resource is effectively identified by its citation information. Thus for a journal article the value of a dcterms:bibliographicCitation property should contain at a minimum: the journal title (or some other identifier of the journal); the volume and issue or part numbers as appropriate; the start page number, or some other identification within the journal issue for an electronic-only article. It is probably also sensible to provide: the full pagination information, i.e. to include the last page number; and the date of publication, even though this may be repeating the value of a separate dcterms:issued property. Some sample plain text citations are in Example 3.


Example 3. Example Text Citations


2.3 Machine Parsable Citations

Recommendation 4. For machine-readable citations use an OpenURL ContextObject.

The provision of a machine parsable citation is encouraged to promote digital interoperability.

The 'OpenURL Framework for Context-Sensitive Services' is the ANSI/NISO standard, Z39.88-2004. It provides a way to describe a referenced resource, bundled together with the associated resources that comprise the context of the reference. This package is called a 'ContextObject'. The standard also defines flavours of 'OpenURL', which are methods of transporting these descriptions between networked systems. The ContextObject is the 'payload' of an OpenURL, but may also be an autonomous data object, and thus the value of a Dublin Core property. Further details of the OpenURL Framework standard are given in Appendix A.

Currently the OpenURL Framework defines metadata formats in its initial registry [7], and hence as part of the standard, for: journals and parts of journals; books and parts of books, including conference proceedings and papers, reports and simple documents; dissertations; and patents. It is probable that more metadata formats will be defined in the future.

These metadata formats are available as both Key/Encoded-Value (KEV) and XML formats. Use of the XML format will be described in a future document. But for many uses, other than XML applications, the KEV format will be the most appropriate. The KEV format is a string of 'ampersand'-delimited pairs, each pair consisting of a label, or key, and an associated value, separated by an 'equals'. The value is 'URL-encoded', which means that special characters are translated into their equivalent hexadecimal byte strings to prevent their misinterpretation when transported by HTTP (e.g. '/' becomes '%2F', ':' becomes '%3A').

Examples 4 and 6 show the keys and values for bibliographic citation information for the same journal article and conference paper as in Examples 1 and 2. Examples 5 and 7 show the complete URL-encoded ContextObject for the same examples, within a bibliographicCitation property encoded in XHTML. Example 5 also includes the journal ISSN as a value URI of a dcterms:isPartOf property. These examples include what are probably the most commonly used ContextObject keys to describe the resource, the 'referent' in OpenURL Framework terminology. The full metadata formats are defined in the OpenURL Registry [7], these examples using the journal metadata format [8] and the book metadata format [9]. There are more examples in the KEV Implementation Guidelines [10]. Optionally the ContextObject could contain further details such as the article title and authors, but these are redundant within a Dublin Core description. Note that because of Recommendation 3 there should be sufficient information within the ContextObject to identify the resource.

Optionally the ContextObject may include a 'referrer', that is the originator of the ContextObject, thus indicating its provenance. In the examples the referrer is the Zetoc current awareness and document delivery service. A referrer is identified as a URI within the 'info:sid/' scheme using the DNS name of the service, followed optionally by the database name, e.g. info:sid/mimas.ac.uk:zetoc.

The KEV ContextObject used here to describe a citation is identified by a URI 'info:ofi/fmt:kev:mtx:ctx'. In the XHTML examples, for consistency with the guidelines for expressing Dublin Core in XHTML, it is referenced as an element 'ctx' of a schema 'info:ofi/fmt:kev:mtx:' named 'KEV'. The required declaration is shown at the beginning of Example 5.

In Dublin Core Abstract Model [11] terms the value of the dcterms:bibliographicCitation property is a value string, encoded according to a KEV ContextObject encoding scheme. It is not intended to be the resource identifier, which for a journal article would probably use an appropriate URI scheme such as DOI


Example 4. ContextObject Keys and Values for a Journal Article

Key Value Description
ctx_ver Z39.88-2004 Version of ContextObject specification
rft_val_fmt info:ofi/fmt:kev:mtx:journal Referent is described using KEV journal metadata format
rft.jtitle Library and Information Science Research Referent journal title
rft.stitle LISR Referent journal abbreviated title
rft.volume 22 Referent volume number
rft.issue 3 Referent issue number
rft.spage 311 Referent start page
rfr_id info:sid/mimas.ac.uk:zetoc Referrer identifier

Example 5. Bibliographic Citation Dublin Core Properties for a Journal Article

<link rel="schema.DCTERMS" href="http://purl.org/dc/terms/" />
<link rel="schema.KEV" href="info:ofi/fmt:kev:mtx:" />

<meta name="DCTERMS.bibliographicCitation" 
content="Library and Information Science Research 22(3), 311-338" />

<meta name="DCTERMS.bibliographicCitation" scheme="KEV.ctx"
content="&ctx_ver=Z39.88-2004
&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Ajournal
&rft.jtitle=Library+and+Information+Science+Research&rft.stitle=LISR
&rft.volume=22&rft.issue=3&rft.spage=311
&rfr_id=info%3Asid%2Fmimas.ac.uk%3Azetoc" />

<link rel="DCTERMS.isPartOf" href="urn:ISSN:0740-8188" />

[Note: line breaks within 'content' are for presentation only. The ContextObject should be a single unbroken line.]


Example 6. ContextObject Keys and Values for a Conference Paper

Key Value Description
ctx_ver Z39.88-2004 Version of ContextObject specification
rft_val_fmt info:ofi/fmt:kev:mtx:book Referent is described using KEV book metadata format
rft.btitle Proceedings of the International Conference on Dublin Core and metadata for e-communities, 2002; DC-2002: Metadata for e-Communities: Supporting Diversity and Convergence, Florence, Italy, 13-17 October 2002 Referent proceedings (book) title
rft.spage 71 Referent start page
rft.isbn 8884530431 Referent ISBN
rfr_id info:sid/mimas.ac.uk:zetoc Referrer identifier

Example 7. Bibliographic Citation Dublin Core Properties for a Conference Paper

<link rel="schema.DCTERMS" href="http://purl.org/dc/terms/" />
<link rel="schema.KEV" href="info:ofi/fmt:kev:mtx:" />

<meta name="DCTERMS.bibliographicCitation" 
content="Proceedings of the International Conference on 
Dublin Core and metadata for e-communities, 2002;
DC-2002: Metadata for e-Communities:
Supporting Diversity and Convergence, Florence, Italy, 13-17 October 2002, pp 71-80" />

<meta name="DCTERMS.bibliographicCitation" scheme="KEV.ctx"
content="&ctx_ver=Z39.88-2004
&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook
&rft.btitle=Proceedings+of+the+International+Conference+on+Dublin+Core+and+
metadata+for+e-communities%2C+2002%3B+DC-2002%3A+Metadata+for+e-Communities
%3A+Supporting+Diversity+and+Convergence%2C+Florence%2C+Italy%2C+13-17+October+2002
&rft.spage=71&rft.isbn=8884530431&rfr_id=info%3Asid%2Fmimas.ac.uk%3Azetoc" />

[Note: line breaks within 'content' are for presentation only. The ContextObject should be a single unbroken line.]


2.4 Citations as References

Recommendation 5. Use dcterms:references to capture the citation information for a reference from a resource.

The bibliographic details of another resource that is referenced by a described resource may be captured as the value of a dcterms:references property, which is an element refinement of dc:relation. The above Recommendations 3 and 4 for encoding the value of dcterms:bibliographicCitation also apply to the value of dcterms:references. However it is probable that further details would be included, such as the title and authors of the referenced resource, if available, mirroring the text of the reference in the citing resource. Example 8 shows, in tabular form, metadata for a journal article that includes two of its references. Examples 9 and 10 each show a single reference to a journal article encoded in XHTML, the first being a plain text citation and the second a value string that is encoded as a OpenURL ContextObject.

Unlike the bibliographic details of the resource itself, a reference should be supplied as either a plain text citation for human reading or an OpenURL ContextObject for machine reading. It is not appropriate to supply duplicate references because there is no way to correlate two differently encoded instances of a single reference.


Example 8. A Journal Article with some References.

Note that the OpenURL ContextObjects are not URL-encoded and include line breaks for clarity.

Property Syntax Encoding Scheme URI Value String Value URI
dc:title   Prototyping Digital Library Technologies in zetoc  
dc:creator   Apps, A  
dc:creator   MacIntyre, R  
dc:publisher   Springer-Verlag  
dcterms:issued http://purl.org/dc/terms/W3CDTF 2002  
dcterms:isPartOf     urn:ISSN:0302-9743
dcterms:bibliographicCitation   Lecture Notes in Computer Science 2458, 309-323 (2002)  
dcterms:bibliographicCitation info:ofi/fmt:kev:mtx:ctx &ctx_ver=Z39.88-2004
&rft_val_fmt=info:ofi/fmt:kev:mtx:journal
&rft.jtitle=Lecture Notes in Computer Science
&rft.volume=2458
&rft.spage=309
 
dcterms:references info:ofi/fmt:kev:mtx:ctx &ctx_ver=Z39.88-2004
&rft_val_fmt=info:ofi/fmt:kev:mtx:journal
&rft.aulast=Apps
&rft.auinit=A
&rft.atitle=zetoc: A Dublin Core Based Current Awareness Service
&rft.jtitle=Journal of Digital Information
&rft.volume=2
&rft.issue=2
&rft.date=2002
 
dcterms:references info:ofi/fmt:kev:mtx:ctx &ctx_ver=Z39.88-2004
&rft_val_fmt=info:ofi/fmt:kev:mtx:journal
&rft.aulast=Carnall
&rft.auinit=D
&rft.atitle=Website of the week: Email alerting services
&rft.jtitle=British Medical Journal
&rft.volume=324
&rft.spage=56
&rft.date=2002
 

Example 9. Reference to a Journal Article as a Plain Text Citation Encoded in XHTML

<meta name="DCTERMS.references" 
content="Apps , A., MacIntyre, R. zetoc: A Dublin Core Based Current Awareness Service. 
Journal of Digital Information (2) (2002)" />

Example 10. Reference to a Journal Article as an OpenURL ContextObject Encoded in XHTML

<link rel="schema.DCTERMS" href="http://purl.org/dc/terms/" />
<link rel="schema.KEV" href="info:ofi/fmt:kev:mtx:" />

<meta name="DCTERMS.references" scheme="KEV.ctx"
content="&ctx_ver=Z39.88-2004
&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Ajournal
&rft.aulast=Carnall&rft.auinit=D
&rft.atitle=Website+of+the+week%3A+Email+alerting+services 
&rft.jtitle=British+Medical+Journal
&rft.volume=324&rft.spage=56&rft.date=2002" />

[Note: line breaks within 'content' are for presentation only. The ContextObject should be a single unbroken line.]


3 Bibliographic Citations in Simple Dublin Core

There are no recommendations for providing bibliographic citations in simple Dublin Core. Simple Dublin Core does not include the concept of an encoding scheme or controlled vocabulary to constrain the value of a property, all values being considered plain text value strings. This precludes providing machine readable details in simple Dublin Core, except by local convention. It is suggested that within a simple Dublin Core description the bibliographic citation information be included in one of:

A KEV OpenURL ContextObject could be included as the value of a simple Dublin Core dc:identifier property, alongside a parallel plain text citation, as shown in Example 11, to provide some possibility, but no guarantee, of machine understanding. When used within an XHTML encoding, as indicated in the DCMI Abstract Model document Appendix D, the value of DC.identifier is a value string even if it looks like a URI, or part of one, to a human reader.


Example 11. Simple Dublin Core Bibliographic Citation for a Journal Article

<meta name="DC.identifier" 
content="Library and Information Science Research 22(3), 311-338" />

<meta name="DC.identifier"
content="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Ajournal
&rft.issn=0740-8188&rft.volume=22&rft.issue=3&rft.spage=311&rfr_id=info%3Asid%2Fmimas.ac.uk%3Azetoc" />

[Note: line breaks within 'content' are for presentation only. The ContextObject should be a single unbroken line.]


Citation information for another resource referenced by a resource described in simple Dublin Core could be captured as the string value of a dc:relation property. Again this could be captured using a KEV ContextObject provided as a value string.


Example 12. Simple Dublin Core Reference to a Journal Article as an OpenURL ContextObject Encoded in XHTML

<meta name="DC.relation"
content="ctx_ver=Z39.88-2004
&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Ajournal
&rft.aulast=Carnall&rft.auinit=D
&rft.atitle=Website+of+the+week%3A+Email+alerting+services 
&rft.jtitle=British+Medical+Journal
&rft.volume=324&rft.spage=56&rft.date=2002" />

[Note: line breaks within 'content' are for presentation only. The ContextObject should be a single unbroken line.]


4 Encoding Bibliographic Citations in XML

Recommendations for encoding bibliographic citation information in XML will be provided in a future document.

As suggested above in the Introduction, for applications that require a complex XML metadata description other metadata schemes that are specifically designed for bibliographic items, such as the OpenURL Framework [1], PRISM [2], MODS [3], or NLM Data [4], would be more appropriate.

5 Other Issues

Several other issues related to describing bibliographic citation information in Dublin Core have been identified.

5.1 Author Affiliation

Recommendation 6. Capture authors' affiliations using dc:contributor.

For a bibliographic resource, in particular a journal article, an author's affiliation is a significant item of information, for resource discovery (e.g. 'find all articles about magnesium published by members of The University of Manchester') as well as for resource description. The affiliation for a journal article or conference paper pertains to the resource. It is the author's affiliation when they created the resource, and will persist even if the author moves to a different institution. Thus it is a property of the resource rather than of the author. It is suggested that this affiliation be captured as the value of a dc:contributor property, recognising that the author's institution will have contributed to the creation of the resource. Because affiliation is a property of the resource, rather than a creator, the fact that there is no way to correlate particular authors with their affiliations (when there are multiple authors) is not an issue.


Example 13. A Dublin Core Description of a Conference Paper including the Authors' Affiliation

Property Value String Value URI
dc:title Exposing Cross-Domain Resources for Researchers and Learners  
dc:creator Apps, A  
dc:creator MacIntyre, R  
dc:contributor MIMAS, The University of Manchester  
dc:publisher Firenze University Press  
dcterms:issued 2002  
dcterms:isPartOf   urn:ISBN:8884530431
dcterms:bibliographicCitation Proceedings of the International Conference on Dublin Core and metadata for e-communities, 2002; DC-2002: Metadata for e-Communities: Supporting Diversity and Convergence, Florence, Italy, 13-17 October 2002, pp 71-80  

5.2 Identifiers

Recommendation 7. Global identifiers should be encoded as URIs.

There are various global identifiers relevant to bibliographic resources, for example ISSN for serials, ISBN for books, SICI (Serial Item and Contribution Identifier), Digital Object Identifier (DOI). They should be encoded in values of Dublin Core properties as value URIs. Table 1 lists some of these identifiers. Some of these identifiers use the new 'info' URI scheme [12]. Until the introduction of this scheme there was no global URI namespace for these identifiers in common use for bibliographic resources.

Table 1. Identifiers for Bibliographic Resources.

IdentifierURI namespace Example
ISSN urn:ISSN: urn:ISSN:0302-9743
ISBN urn:ISBN: urn:ISBN:8884530431
NBN (National Bibliographic Number) urn:NBN: urn:NBN:fi-fe19981001
Digital Object Identifier info:doi/ info:doi/10.1045/july99-caplan
SICI info:sici/ info:sici/07408188(200010)22:3%3C311:SEUB%3E2.0.CO;2-X
PubMed info:pmid/ info:pmid/9036860
Open Archives Initiative info:oai/ info:oai/arXiv.org:hep-th/9901001

5.3 Electronic-only Articles

The recommendations given above to describe the bibliographic citation information for a journal article assume that the article is published within a printed journal issue and is identified within that issue by its start page. Although the majority of journal articles are now available electronically, they are still packaged within an issue with the notion of a start page (in fact they are still published in print as well as electronically). But increasingly there are 'born digital' electronic journals that do not have a parallel print version, where the concept of a page number does not exist. And some journal articles in rapidly developing fields are published in advance of being assigned to a journal issue. Thus to describe an electronic-only journal article some identification of the article, either within a journal issue, or stand-alone, is required. This identification will be depend on the particular article and circumstances of its publication. For an article in an electronic journal that is published by issue there will be some identification of the article within the issue, as in Example 14. It will be more appropriate to describe some electronic articles by an identifier, such as a digital object identifier (DOI), if available, or by a URL that points to a location where the article may be read.


Example 14. The Bibliographic Citation for an Electronic Journal Article.

Property Value String Value URI Resource URI
dc:title Open Linking in the Scholarly Information Environment Using the OpenURL Framework    
dc:creator Van de Sompel, H    
dc:creator Beit-Arie, O    
dcterms:issued 2001    
dc:identifier     info:doi/10.1045/march2001-vandsompel
dcterms:isPartOf   urn:ISSN:1082-9873  
dcterms:bibliographicCitation D-Lib Magazine 7(3), march2001-vandesompel    

5.4 Resource Type

It may be desirable to indicate the resource type of a bibliographic item, e.g. journal article, conference paper. It is suggested that a dc:type property be used with a term from a recognised vocabulary as its value.


Example 15. A Resource Type Indicating a Journal Article

<meta name="DC.type" scheme="DCTERMS.MESH" content="Journal Article [Publication Type]" />

5.5 Previous Proposals from the DCMI Citation Working Group

The DCMICite Dublin Core Structured Value is deprecated.

During its lifetime the DCMI Citation Working Group proposed a Dublin Core Structured Value (DCSV), DCMICite, to capture bibliographic citation information in a machine parsable, but also human readable, form. Versions of this proposal were published in various papers and used in several implementations, primarily because there were no other recommendations to follow. This proposal is now deprecated and should not be used, except in local applications. Because it was not endorsed by the DCMI Usage Board, use of DCMICite cannot guarantee future interoperability. The proposal was based on DCSV, a syntax that is also deprecated. It is no longer needed for bibliographic citation description, OpenURL Framework metadata formats now being available to supersede it.

Appendix A. The OpenURL Framework for Context-Sensitive Services

The 'OpenURL Framework for Context-Sensitive Services' is the ANSI/NISO standard, Z39.88-2004 [1]. It provides a way to describe a referenced resource, bundled together with the associated resources that comprise the context of the reference. This package is called a 'ContextObject'. The standard also defines flavours of 'OpenURL', which are methods of transporting these descriptions between networked systems. The ContextObject is the 'payload' of an OpenURL, but may also be an autonomous data object.

Typically, in a digital library context, a user will click on an OpenURL link in an HTML page, for example beside a citation within the reference list of an electronic journal article. The OpenURL for the reference will be passed to a linking server or resolver, which will return to the user a selection of resources pertinent to the cited article, preferably including a link to an appropriate copy of the full text of the article.

A ContextObject may contain up to six entities. One of these, the 'referent', holds information about the referenced resource. It must always be included in a ContextObject. The other five entities are: the resource where the reference occurs (referring entity); the user (requester); the service to which a request is sent (resolver); the service that generated the OpenURL (referrer); and the type of service requested.

Within the ContextObject, information about each entity may be detailed in four ways. An identifier within an indicated namespace will define a resource. A set of metadata, encoded as either 'by-value' or 'by-reference' may describe the entity. The difference is that a by-value metadata description is contained within the ContextObject, whereas a by-reference metadata description is held elsewhere at a URI identified in the ContextObject. The fourth type is undefined private data that requires a prior understanding between a resolver and a referrer.

Entities may be encoded in either 'Key / Encoded-Value' (KEV) Format or XML. KEV is a string of 'ampersand'-delimited pairs, each pair consisting of a label, or key, and an associated value, separated by an 'equals'. The value is 'URL-encoded', which means that special characters are translated into their equivalent hexadecimal byte strings to prevent their misinterpretation when transported by HTTP.

The OpenURL Framework is very general and has the potential to be used in many application domains and by many communities. Its core components are defined within the OpenURL Registry [7]. It includes lists of identifier namespaces and metadata formats. A selection from the Registry of a consistent set of components appropriate to a particular application domain is a 'Community Profile', also defined in the Registry.

More details and explanation of the OpenURL Framework may be found in the KEV Implementation Guidelines [10] and in the standard [1] itself.

References

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