WEBDAV Working Group J. Stracke, eCal Corp. INTERNET DRAFT <draft-ietf-webdav-dublin-core-01> Expires December, 1999 June 8, 1999 Use of Dublin Core Metadata in WebDAV 1 Status of this Document This document is an Internet-Draft and is in full conformance with all provisions of Section 10 of RFC2026. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet-Drafts. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as ``work in progress.'' The list of current Internet-Drafts can be accessed at <http://www.ietf.org/ietf/1id-abstracts.txt> The list of Internet-Draft Shadow Directories can be accessed at <http://www.ietf.org/shadow.html> Distribution of this document is unlimited. Please send comments to francis@ecal.com or to the w3c-dist-auth@w3.org discussion list. 2 Abstract This document specifies a mapping for using the metadata vocabulary of Dublin Core ([DUBLIN]) in a WebDAV ([WEBDAV]) server. 3 Introduction This document specifies a mapping for using the metadata vocabulary of Dublin Core ([DUBLIN]) in a WebDAV ([WEBDAV]) server. WebDAV defines a protocol for manipulating metadata on a Web resource; in WebDAV, an element of metadata is called a property. Dublin Core defines several metadata elements, with standard names and standard meanings. A server which stores Dublin Core metadata for its content may wish to make the metadata available as WebDAV properties; to forestall the emergence of incompatible ways to provide this functionality, this document defines a mapping from Dublin Core element labels into WebDAV property names. The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALLNOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and"OPTIONAL" in this document are to be interpreted as described in [MUSTS] . 4 Mapping The approach taken in this mapping is to leverage the RDF encoding Stracke [Page 1]
INTERNET-DRAFT Dublin Core in WebDAV June 8, 1999 ([DC-RDF]) of Dublin Core. An [RDF] document encoding Dublin Core data would look something like this: <?xml version="1.0"?> <rdf:RDF xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#" xmlns:dc="http://purl.org/dc/elements/1.0/" xmlns:dcq="http://purl.org/dc/qualifiers/1.0/"> <rdf:Description about="http://www.ietf.org/rfc/rfc822.txt"> <dc:creator> <rdf:Description> <rdf:value>Crocker, David</rdf:value> <dcq:creatorType rdf:resource="http://purl.org/dc/schema/LastnameFirstname#"/> </rdf:Description> </dc:creator> </rdf:Description> </rdf:RDF> The mapping defined here works by identifying each subelement of <rdf:Description> with a single WebDAV property. Since WebDAV properties are expressed as XML elements ([XML]), using XML namespaces ([XMLNS]) allow different groups to define sets of properties without interfering with each other, the mapping is direct and one-to-one. In this case, the namespaces being used are <URI:http://purl.org/dc/elements/1.0/>, <URI:http://purl.org/dc/qualifiers/1.0/>, and <URI:http://www.w3.org/1999/02/22-rdf-syntax-ns#>, as specified in [RDF] and [DC-RDF]. To obtain the Dublin Core creator for the resource <http://www.ietf.org/rfc/rfc822.txt>, a WebDAV client would issue a PROPFIND method to the resource, requesting the dc:creator property: PROPFIND /rfc/rfc822.txt HTTP/1.1 Host: www.ietf.org Content-type: text/xml; charset="utf-8" Content-Length: xxxx <?xml version="1.0" encoding="utf-8" ?> <D:propfind xmlns:D="DAV:"> <D:prop xmlns:dc="http://purl.org/dc/elements/1.0/"> <dc:creator/> </D:prop> </D:propfind> The response to the request would provide the <dc:creator> element, and all its contents, just as in the RDF document above. 4.1 Correspondences The following table illustrates the relationship between [DUBLIN] element names and [WEBDAV] property names. The dc: prefix is assumed to be mapped to the namespace http://purl.org/dc/elements/1.0/. Stracke [Page 2]
INTERNET-DRAFT Dublin Core in WebDAV June 8, 1999 Dublin Core element WebDAV property DC.Title dc:title DC.Creator dc:creator DC.Subject dc:subject DC.Description dc:description DC.Publisher dc:publisher DC.Contributor dc:contributor DC.Date dc:date DC.Type dc:type DC.Format dc:format DC.Identifier dc:identifier DC.Source dc:source DC.Language dc:language DC.Relation dc:relation DC.Coverage dc:coverage DC.Rights dc:rights 4.2 Abbreviated Syntax The Abbreviated Syntax of [DC-RDF] MUST NOT be used in this encoding, since it requires packing separate properties into a single XML element, which is incompatible with the DAV property model. 4.3 Complications A previous version of this document had some difficulties with advanced sections of the Dublin Core model. This version addresses these problems, but it may be useful to enumerate them for future reference. 4.3.1 Multivalued Properties A WebDAV property can occur on a resource only once, while a content item may bear more than one instance of a Dublin Core element. The previous document defined an ad hoc XML syntax for listing multiple values, which drew criticism from people who wanted more general multivalued property support for WebDAV. This document is able to sidestep the problem because Dublin Core now has its own solution, and it is not necessary to create a new one. In the above example, if RFC-822 had multiple authors, the <dc:creator> element might contain an <rdf:Bag> element containing <rdf:li> elements. 4.3.2 Qualification (Subelements) When the previous document was written, some members of the Dublin Core group had plans to support more structure in their metadata, but had not yet defined a syntax for it. At this time, the debate over subelements is still not fully resolved, but the syntax in the RDF encding has been established: to add extra data on a dc: element, one nests a dcq: element within it, as a qualifier, as in the <dcq:creatorType> element in the RDF example above. Stracke [Page 3]
INTERNET-DRAFT Dublin Core in WebDAV June 8, 1999 5 Examples The examples in this section are based on Example 14 of [DC-RDF], showing how [WEBDAV] would be used to set and get the properties presented there. (Note that non-ASCII characters in Example 14 have been elided for the sake of the ASCII Internet-Draft format.) 5.1 Set with PROPPATCH 5.1.1 Request PROPPATCH /metadata/resources/dc/datamodel/WD-dc-rdf/ HTTP/1.1 Host: www.ukoln.ac.uk Content-type: text/xml Content-length: xxxx <?xml version="1.0"?> <D:propertyupdate xmlns:D="DAV:" xmlns:dc="http://purl.org/dc/elements/1.0/" > <D:set> <D:prop> <rdf:Description rdf:about="http://www.ukoln.ac.uk/metadata/resources/dc/datamodel/ WD-dc-rdf/"> <dc:title> <rdf:Alt> <rdf:li xml:lang="en">Guidance on expressing the Dublin Core within the Resource Description Framework (RDF)</rdf:li> <rdf:li xml:lang="no">Veiledning a uttrykke Dublin Core innenfor rammen av Resource Description Framework (RDF)</rdf:li> <rdf:li xml:lang="de">Dublin Core in RDF: Eine Anleitung</rdf:li> </rdf:Alt> </dc:title> <dc:creator> <rdf:Bag> <rdf:li>Eric Miller</rdf:li> <rdf:li>Paul Miller</rdf:li> <rdf:li>Dan Brickley</rdf:li> </rdf:Bag> </dc:creator> <dc:description> <rdf:Alt> <rdf:li xml:lang="en">This document describes work carried out by the Data Model Working Group of the Dublin Core Metadata Initiative. Specifically, the document discusses means by which the fifteen elements of the Dublin Core (as defined in RFC 2413) may be expressed using the Resource Description Framework (RDF) and encoded with the eXtensible Markup Language (XML). RDF-based mechanisms by which the 15 elements may be qualified are also introduced.</rdf:li> <rdf:li xml:lang="no">Dette dokumentet beskriver arbeide utfort av Stracke [Page 4]
INTERNET-DRAFT Dublin Core in WebDAV June 8, 1999 arbeidsgruppen for datamodellering knyttet til Dublin Core-initiativet. Spesifikt diskuterer dokumentet hvordan de femten elementene i Dublin Core (slik disse er definert i RFC 2413) kan uttrykkes ved hjelp av Resource Description Framework (RDF) og kodes ved hjelp av eXtensible Markup Language (XML). Videre introduseres RDF-baserte mekanismer for a kvalifisere de 15 elementene.</rdf:li> </rdf:Alt> </dc:description> <dc:subject> Dublin Core; Resource Description Framework; RDF; eXtensible Markup Language; XML </dc:subject> <dc:publisher> Dublin Core Metadata Initiative </dc:publisher> <dc:contributor> Dublin Core Data Model Working Group </dc:contributor> <dc:date> <rdf:Description> <dcq:dateScheme> WTN8601 </dcq:dateScheme> <rdf:value> 1999-05-26 </rdf:value> </rdf:Description> </dc:date> <dc:format> <rdf:Description> <dcq:formatScheme> IMT </dcq:formatScheme> <rdf:value> text/html </rdf:value> </rdf:Description> </dc:format> <dc:language> <rdf:Description> <dcq:languageScheme> RFC1766 </dcq:languageScheme> <rdf:value> en </rdf:value> </rdf:Description> </dc:language> </rdf:Description> <D:/prop> <D:/set> </D:propertyupdate> 5.1.2 Response HTTP/1.1 200 OK 5.2 Retrieving a single Dublin Core property with PROPFIND This example shows how to fetch the DC.Title property. 5.2.1 Request PROPFIND /metadata/resources/dc/datamodel/WD-dc-rdf/ HTTP/1.1 Host: www.ukoln.ac.uk Content-type: text/xml; charset="utf-8" Content-Length: xxxx <?xml version="1.0" encoding="utf-8" ?> Stracke [Page 5]
INTERNET-DRAFT Dublin Core in WebDAV June 8, 1999 <D:propfind xmlns:D="DAV:"> <D:prop xmlns:dc="http://purl.org/dc/elements/1.0/"> <dc:title/> </D:prop> </D:propfind> 5.2.2 Response HTTP/1.0 200 OK Content-Type: text/xml Content-Length: xxxx <?xml version="1.0" ?> <D:propstat xmlns:D="DAV:" xmlns:dc="http://purl.org/dc/elements/1.0/" > <prop> <dc:title> <rdf:Alt> <rdf:li xml:lang="en">Guidance on expressing the Dublin Core within the Resource Description Framework (RDF)</rdf:li> <rdf:li xml:lang="no">Veiledning a uttrykke Dublin Core innenfor rammen av Resource Description Framework (RDF)</rdf:li> <rdf:li xml:lang="de">Dublin Core in RDF: Eine Anleitung</rdf:li> </rdf:Alt> </dc:title> </prop> </propstat> 5.3 Retrieving multiple Dublin Core properties with PROPFIND This example shows how to fetch the DC.Title, DC.Creator, and DC.Publisher properties in a single request. 5.3.1 Request PROPFIND /metadata/resources/dc/datamodel/WD-dc-rdf/ HTTP/1.1 Host: www.ukoln.ac.uk Content-type: text/xml; charset="utf-8" Content-Length: xxxx <?xml version="1.0" encoding="utf-8" ?> <D:propfind xmlns:D="DAV:"> <D:prop xmlns:dc="http://purl.org/dc/elements/1.0/"> <dc:title/> <dc:creator/> <dc:publisher/> </D:prop> </D:propfind> 5.3.2 Response Stracke [Page 6]
INTERNET-DRAFT Dublin Core in WebDAV June 8, 1999 HTTP/1.0 200 OK Content-Type: text/xml Content-Length: xxxx <?xml version="1.0" ?> <D:propstat xmlns:D="DAV:" xmlns:dc="http://purl.org/dc/elements/1.0/" > <prop> <dc:title> <rdf:Alt> <rdf:li xml:lang="en">Guidance on expressing the Dublin Core within the Resource Description Framework (RDF)</rdf:li> <rdf:li xml:lang="no">Veiledning a uttrykke Dublin Core innenfor rammen av Resource Description Framework (RDF)</rdf:li> <rdf:li xml:lang="de">Dublin Core in RDF: Eine Anleitung</rdf:li> </rdf:Alt> </dc:title> <dc:creator> <rdf:Bag> <rdf:li>Eric Miller</rdf:li> <rdf:li>Paul Miller</rdf:li> <rdf:li>Dan Brickley</rdf:li> </rdf:Bag> </dc:creator> <dc:publisher> Dublin Core Metadata Initiative </dc:publisher> </prop> </propstat> 6 Internationalization Considerations XML is an inherently internationalizable format, able to express any language or character set; as a result, all WebDAV properties, including the Dublin Core properties defined here, are internationalizable. 7 Security Considerations The security considerations of this mapping are those of [DUBLIN] plus those of [WEBDAV]. 8 IANA Considerations The namespace defined here is isomorphic to the element namespace defined in [DUBLIN], so this document introduces no new IANA considerations beyond those of [DUBLIN]. Stracke [Page 7]
INTERNET-DRAFT Dublin Core in WebDAV June 8, 1999 9 Copyright The following copyright notice is copied from RFC 2026 [Bradner, 1996], section 10.4, and describes the applicable copyright for this document. Copyright (C) The Internet Society April 5, 1998. All Rights Reserved. This document and translations of it may be copied and furnished to others, and derivative works that comment on or otherwise explain it or assist in its implementation may be prepared, copied, published and distributed, in whole or in part, without restriction of any kind, provided that the above copyright notice and this paragraph are included on all such copies and derivative works. However, this document itself may not be modified in any way, such as by removing the copyright notice or references to the Internet Society or other Internet organizations, except as needed for the purpose of developing Internet standards in which case the procedures for copyrights defined in the Internet Standards process must be followed, or as required to translate it into languages other than English. The limited permissions granted above are perpetual and will not be revoked by the Internet Society or its successors or assignees. This document and the information contained herein is provided on an "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. 10 Intellectual Property The following notice is copied from RFC 2026 [Bradner, 1996], section 10.4, and describes the position of the IETF concerning intellectual property claims made against this document. The IETF takes no position regarding the validity or scope of any intellectual property or other rights that might be claimed to pertain to the implementation or use other technology described in this document or the extent to which any license under such rights might or might not be available; neither does it represent that it has made any effort to identify any such rights. Information on the IETF's procedures with respect to rights in standards-track and standards-related documentation can be found in BCP-11. Copies of claims of rights made available for publication and any assurances of licenses to be made available, or the result of an attempt made to obtain a general license or permission for the use of such proprietary rights by implementors or users of this specification can be obtained from the IETF Secretariat. Stracke [Page 8]
INTERNET-DRAFT Dublin Core in WebDAV June 8, 1999 The IETF invites any interested party to bring to its attention any copyrights, patents or patent applications, or other proprietary rights which may cover technology that may be required to practice this standard. Please address the information to the IETF Executive Director. 11 Acknowledgements The triviality of this specification is due to the hard work put into [WEBDAV], [DUBLIN], [XML], and [XMLNS] by their respective authors and working groups. The need for this specification was pointed out (by Jim Whitehead, I think) during the variants discussion held after a meeting of the versioning design team of the WebDAV working group. Thanks to Liz Parrot for alerting me to the question of subelements. Thanks to Paul Miller for clarifying to me how [DC-RDF] handles multivalued properties. 12 References 12.1 Normative References [DUBLIN] S. Weibel, J. Kunze, C. Lagoze, M. Wolf, "Dublin Core Metadata for Resource Discovery." RFC 2413. Online Computer Library Center; University of California, San Francisco; Cornell; Reuters. September, 1998. [WEBDAV] Y. Y. Goland, E. J. Whitehead, Jr., A. Faizi, S. R. Carter, D. Jensen, "Extensions for Distributed Authoring on the World Wide Web - WebDAV." RFC 2518. Microsoft, U.C. Irvine, Netscape, Novell. April, 1998. [XML] T. Bray, J. Paoli, C. M. Sperberg-McQueen, "Extensible Markup Language (XML)." World Wide Web Consortium Recommendation Rec-xml-19980210. <http://www.w3.org/TR/1998/REC-xml-19980210>. [RDF] Resource Description Framework Model and Syntax Specification, February 1999, World Wide Web Consortium Recommendation Rec-rdf-syntax/. <http://www.w3.org/TR/1998/REC-rdf-syntax/>.. [DC-RDF] E. Miller, P. Miller, D. Brickley, "Guidance on expressing the Dublin Core within the Resource Description Framework", May 1999, http://www.ukoln.ac.uk/metadata/resources/dc/datamodel/WD-dc-rdf/ [MUSTS] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels," RFC 2119, Harvard University, March 1997. 12.2 Informational References [XMLNS] T. Bray, D. Hollander, A. Layman, "Name Spaces in XML" World Stracke [Page 9]
INTERNET-DRAFT Dublin Core in WebDAV June 8, 1999 Wide Web Consortium Working Draft, <http://www.w3.org/TR/WD-xml-names>. [GUENTHER] R. Guenther, "Dublin Core Qualifiers/Substructure", <http://www.loc.gov/marc/dcqualif.html>. October, 1997. 13 Authors' Addresses J. Stracke eCal Corp. 234 N. Columbus Blvd., 2nd Floor francis@ecal.com Stracke [Page 10]
