Internet DRAFT - draft-christian-prop-semantics
draft-christian-prop-semantics
WEBDAV Working Group E. Christian
INTERNET DRAFT U.S. Geological Survey
Expires October, 2000 April 24, 2000
<draft-christian-prop-semantics-00.txt>
Use of a Semantics Register with WebDAV Properties
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
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and may be updated, replaced, or obsoleted by other documents at any
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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
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2. Abstract
This document specifies a mechanism to associate a WebDAV ([WEBDAV])
property with an entry in a Semantics Register. A Semantics Register
documents the meaning of properties in a formal manner and may be
implemented with schema technologies such as Extensible Markup
Language (XML) Schema ([XMLSCHEMA]) or Resource Description Framework
(RDF) Schema ([RDFS]). Schema technologies expose the derivation of
complex properties from simpler concepts, as demonstrated in the Basic
Semantics Register ([BSR]) for data elements used in Electronic Data
Interchange. Registering the meanings of properties in this manner can
enhance interoperability across systems and throughout the long-term
information life cycle.
3. Introduction
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [MUSTS] .
This document specifies how a WebDAV ([WEBDAV]) property can be
associated with an entry in a Semantics Register. The Semantics
Register may be implemented with schema technologies such as XML
Schema ([XMLSCHEMA]), Resource Description Framework RDF) Schema,
and perhaps others that use the XML Namespaces [XMLNS] mechanism.
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WebDAV defines a protocol for manipulating the contents of properties
in a Web object instance. Each such property is referenced in WebDAV
by a name that is unique within a specific namespace.
It is often important to associate with a property some assertions
in addition to its name and contents: assertions such as alternate
labels or the property's semantic or syntactic relationship to other
properties in the same or other systems. In organizing these
assertions, a Semantics Register serves as an important tool for
documenting a system and enabling interoperability among systems.
When implemented with schema technologies, a Semantics Register can
expose how complex properties are derived from simpler concepts.
This use is demonstrated in the Basic Semantics Register ([BSR]),
wherein thousands of complex data elements used in Electronic Data
Interchange are constructed from commonly understood concepts.
4. Semantics Register referenced through a WebDAV Namespace
A Semantics Register can be referenced within WebDAV through the
XML Namespace ([XMLNS]) attribute. For example, assume there is a
Semantics Register for Open Document Management ([ODMA]) properties
at the URI "http://www.semantics.org/reg/odm.rdfs", and one of the
ODM properties has an attribute ID "ODM_CHECKEDOUTBY". This
hypothetical Semantics Register can be referenced in the value of an
"xmlns" attribute on the "prop" element of a WebDAV "propfind", e.g.,
<?xml version="1.0" encoding="utf-8" ?>
<D:propfind xmlns:D="DAV:">
<D:prop xmlns:odm="http://www.semantics.org/reg/odm.rdfs">
<odm:ODM_CHECKEDOUTBY/>
</D:prop>
</D:propfind>
5. Example Semantics Register
On the Web, a simple Semantics Register can be implemented using XML
Schema ([XMLSCHEMA])or RDF Schema ([RDFS]). For semantic concepts
and data elements, XML Schema employs "Types" and "Elements" where
RDF Schema employs "Classes" and "Properties". Relationships among
these can be defined in either schema technology, so that complex
entities can be formally defined as comprised of simpler entities.
In the RDF Schema technology, every Class or Property is defined by
an "RDF Description". A particular WebDAV property can be associated
with a particular RDF Description by matching the WebDAV property
name with the ID attribute of the RDF Description. From the example
above, the WebDAV property name "odm:ODM_CHECKEDOUTBY" may correspond
to this RDF Description entry in the hypothetical Semantics Register:
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<rdf:Description rdf:ID="ODM_CHECKEDOUTBY">
<rdfs:comment>Username of the person who has the document
checked-out.</rdfs:comment>
</rdf:Description>
Each RDF Description in a schema referenced by a WebDAV namespace
can contain various assertions about the WebDAV property. These
assertions are expressed as RDF Schema elements and attributes.
Assertions about the WebDAV property include label, subClassOf,
subPropertyOf, domain, range, comment, and isDefinedBy, among others.
Here, for example, is a fuller entry for the ODM_CHECKEDOUTBY
property as it might exist in the hypothetical Semantics Register:
<rdf:Description rdf:ID="ODM_CHECKEDOUTBY">
<rdf:type rdf:resource="http://www.w3.org/TR/1999/
PR-rdf-schema-19990303#Property"/>
<rdfs:subPropertyOf rdf:resource="#person"/>
<rdfs:domain rdf:resource="#ODM"/>
<rdfs:range rdf:resource="http://www.w3.org/TR/
xmlschema-2/#string"/>
<rdfs:comment>Username of the person who has the document
checked-out.</rdfs:comment>
</rdf:Description>
6. Internationalization Considerations
The international considerations of the mechanism to associate a
WebDAV property with an entry in a Semantics Register are affected
by both WebDAV and the specific Semantics Register technology used.
WebDAV uses XML ([XML]) and inherits the relatively robust support in
XML for internationalization. The only Semantics Register technology
discussed here is the RDF Schema specification, which also uses XML.
7. Security Considerations
The mechanism to associate WebDAV properties with a Semantics
Register does not itself affect security. Any security considerations
are a function of WebDAV technology and the specific Semantics
Register technology. When implemented using Internet protocols and
data representation techniques, both technologies inherit the
security characteristics of those protocols and techniques.
8. IANA Considerations
The mechanism to associate WebDAV properties with a Semantics
Register does not itself introduce any new IANA considerations.
It makes use of namespaces as they may be defined for WebDAV and for
any particular Semantics Registry technology such as RDF Schema.
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9. Copyright and Intellectual Property
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 of the 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.
11. Acknowledgements
Many groups and individuals contributed to the various technologies
and ideas that form the substance of this Internet-Draft. The author
especially acknowledges the contributions of Jim Whitehead in the
WebDAV area, Eric Miller in the area of RDF, Andrew Layman in XML
Namespaces, Bruce Bargmeyer in Semantics Registers, Denis Hill in
the Basic Semantics Register, and Owen Ambur in the area of Open
Document Management Attributes.
12. References
[BSR] Basic Semantics Register demo (This site is for demonstration
of technology only. The BSR content is under review in ISO).
<http://www.gils.net/bsr>.
[MUSTS] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels," RFC 2119, Harvard University, March 1997.
[ODMA] Open Document Management API (ODMA) version 2.0, May 1998,
Association for Information and Image Management.
<http://www.aiim.org/odma/odma20.htm#document attributes>.
[RDFS] Resource Description Framework (RDF) Schema Specification,
March 1999, World Wide Web Consortium Proposed Recommendation
PR-rdf-schema-19990303.
<http://www.w3.org/TR/1999/PR-rdf-schema-19990303>
[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.
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[XML] Extensible Markup Language (XML) 1.0, February 1998, World
Wide Web Consortium Recommendation Rec-xml-19980210.
<http://www.w3.org/TR/1998/REC-xml-19980210>.
[XMLNS] Namespaces in XML, January 1999, World Wide Web Consortium
Recommendation REC-xml-names-19990114.
<http://www.w3.org/TR/1999/REC-xml-names-19990114>.
[XMLSCHEMA] XML Schema Part 1 - Strctures, April, 2000, World
Wide Web Consortium Working Draft.
<http://www.w3.org/TR/2000/WD-xmlschema-1-20000407/>
13. Expiration
This Internet-Draft expires October 24, 2000.
14. Discussion mailing list
Comments may be sent to the WebDAV mailing list, w3c-dist-auth@w3.org.
15. Author's Address
Eliot Christian
U.S. Geological Survey
802 National Center
Reston, VA 20192
echristi@usgs.gov
Christian [Page 5]
