W3C W3C Member Submission

CBD - Concise Bounded Description

W3C Member Submission 30 September 2004

This version:
http://www.w3.org/submissions/2004/SUBM-CBD-20040930/
Latest version:
http://www.w3.org/submissions/CBD/
Author:
Patrick Stickler, Nokia, patrick.stickler@nokia.com

Copyright Nokia 2003-2004.
This document is available under the W3C Document License. See the W3C Intellectual Rights Notice and Legal Disclaimers for additional information.

Abstract

This document defines a concise bounded description of a resource in terms of an RDF graph, as an optimal unit of specific knowledge about that resource to be utilized by, and/or interchanged between, semantic web agents.

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Table of contents

  1. Introduction
  2. Definition
  3. Example
  4. References

Introduction

As the semantic web [1] emerges and the behavior of automated software agents becomes increasingly directed by formally defined knowledge about resources gathered from disparate sources [2], the need for optimal and consistent interchange of knowledge about specific resources between agents becomes critical to achieving an efficient, globally scalable, and ubiquitous semantic web.

This document defines a concise bounded description of a resource in terms of an RDF graph [3], as an optimal unit of specific knowledge about that resource to be utilized by, and/or interchanged between, semantic web agents.

Representations versus Descriptions

The web, as traditionally defined [4], [5], is concerned with providing representations of resources. Representations can essentially be anything associated with the resource which is considered useful in understanding, accessing, interacting, and/or manipulating that resource. This is fine for visual presentation to humans browsing the web, who can deal with a great amount of variety, inconsistency, and ambiguity while still deriving benefit from the representations provided. It is this flexibility and unconstrained richness of what representations can be that is one of the factors responsible for the tremendous success of the web.

However, semantic web agents (at present at least) are not able to deal as well with the broad range of possible representations which might be associated with a resource; and in nearly all cases, are unable to make any use of such representations, as they are typically intended for human rather than machine consumption. Semantic web agents, not being anywhere near as intelligent as most humans, require information which is explicit and formally defined. In short, semantic web agents need concise, bounded descriptions of resources, expressed in a machine understandable language, rather than seemingly arbitrary representations which to agents are usually semantically opaque.

A concise bounded description of a resource is a body of knowledge about that resource which does not include any explicit knowledge about any other resource which can be obtained separately from the same source.

Concise bounded descriptions of resources can be considered to be a form of representation, however they are a highly specialized form and not the most usual or obvious form in a web primarily intended for human consumption. They are, however, a key form of representation which semantic web agents need in order to reason about such resources and adjust their behavior accordingly.

Definition

A concise bounded description can be defined in terms of an RDF graph as follows:

Given a node in an RDF graph which occurs as the subject of one or more statements in that graph, the concise bounded description of the resource denoted by that node is the subgraph of statements comprised as follows:

  1. Include all statements where the subject of the statement denotes the resource in question; and
  2. Recursively, for all statements included in the description thus far, for all anonymous node objects, include the inverse functional bounded description of the anonymous resource as follows:

    Inverse Functional Bounded Description

    If there exists at least one statement having the anonymous resource as subject and where the predicate is an owl:InverseFunctionalProperty [6], then

    • Include only those statements having the anonymous resource as subject and where the predicate is an owl:InverseFunctionalProperty; and
    • If the object of such a statement is an anonymous node, include the inverse functional bounded description of that anonymous resource.

    Else,

    • Include all statements where the anonymous resource is the subject; and
    • If the object of such a statement is an anonymous node, include the inverse functional bounded description of that anonymous resource.
    and
  3. Recursively, for all statements included in the description thus far, for all reifications of each statement, include the concise bounded description of the rdf:Statement resource of each reification.

This results in an RDF graph where the terminal nodes are either URI references, literals, or anonymous nodes not serving as the subject of any statement, insofar as the original source graph is concerned; effectively constraining the description to only those statements made explicitly about the resource in question or about other directly related anonymous resources, and any associated reifications.

Example

Given the following RDF graph: 


<?xml version="1.0"?>

<rdf:RDF
   xmlns:rdf  ="http://www.w3.org/1999/02/22-rdf-syntax-ns#"
   xmlns:rdfs ="http://www.w3.org/2000/01/rdf-schema#"
   xmlns:owl  ="http://www.w3.org/2002/07/owl#"
   xmlns:dc   ="http://purl.org/dc/elements/1.1/"
   xmlns:dct  ="http://purl.org/dc/terms/"
   xmlns:xsd  ="http://www.w3.org/2001/XMLSchema#"
   xmlns:foaf ="http://xmlns.com/foaf/0.1/">

   <rdf:Description rdf:about="http://example.com/aReallyGreatBook">
      <dc:title>A Really Great Book</dc:title>
      <dc:publisher>Examples-R-Us</dc:publisher>
      <dc:creator>
         <rdf:Description>
            <rdf:type rdf:resource="http://xmlns.com/foaf/0.1/Person"/>
            <foaf:name>John Doe</foaf:name>
            <foaf:mbox>john@example.com</foaf:mbox>
            <foaf:img>
               <rdf:Description rdf:about="http://example.com/john.jpg">
                  <rdf:type rdf:resource="http://xmlns.com/foaf/0.1/Image"/>
                  <dc:format>image/jpeg</dc:format>
                  <dc:extent>1234</dc:extent>
               </rdf:Description>
            </foaf:img>
            <foaf:phone rdf:resource="tel:+1-999-555-1234"/>
         </rdf:Description>
      </dc:creator>
      <dc:contributor>
         <rdf:Description>
            <rdf:type rdf:resource="http://xmlns.com/foaf/0.1/Person"/>
            <foaf:name>Jane Doe</foaf:name>
         </rdf:Description>
      </dc:contributor>
      <dc:language>en</dc:language>
      <dc:format>application/pdf</dc:format>
      <dc:rights>Copyright (C) 2004 Examples-R-Us. All rights reserved.</dc:rights>
      <dct:issued rdf:datatype="http://www.w3.org/2001/XMLSchema#date">2004-01-19</dct:issued>
      <rdfs:seeAlso rdf:resource="http://example.com/anotherGreatBook"/>
   </rdf:Description>

   <rdf:Statement>
      <rdf:subject rdf:resource="http://example.com/aReallyGreatBook"/>
      <rdf:predicate rdf:resource="http://purl.org/dc/elements/1.1/format"/> 
      <rdf:object>application/pdf</rdf:object>
      <rdfs:isDefinedBy rdf:resource="http://example.com/book-formats.rdf"/>
   </rdf:Statement>

   <rdf:Statement>
      <rdf:subject rdf:resource="http://xmlns.com/foaf/0.1/Image"/>
      <rdf:predicate rdf:resource="http://purl.org/dc/elements/1.1/format"/> 
      <rdf:object>image/jpeg</rdf:object>
      <rdfs:isDefinedBy rdf:resource="http://example.com/image-formats.rdf"/>
   </rdf:Statement>

   <rdf:Description rdf:about="http://example.com/anotherGreatBook">
      <dc:title>Another Great Book</dc:title>
      <dc:publisher>Examples-R-Us</dc:publisher>
      <dc:creator>June Doe (june@example.com)</dc:creator>
      <dc:format>application/pdf</dc:format>
      <dc:language>en</dc:language>
      <dc:rights>Copyright (C) 2004 Examples-R-Us. All rights reserved.</dc:rights>
      <dct:issued rdf:datatype="http://www.w3.org/2001/XMLSchema#date">2004-05-03</dct:issued>
      <rdfs:seeAlso rdf:resource="http://example.com/aReallyGreatBook"/>
   </rdf:Description>

   <rdf:Property rdf:about="http://xmlns.com/foaf/0.1/mbox">
      <rdf:type rdf:resource="http://www.w3.org/2002/07/owl#InverseFunctionalProperty"/>
   </rdf:Property>

</rdf:RDF>

The concise bounded description of the resource http://example.com/aReallyGreatBook corresponds to the following subgraph: 


<?xml version="1.0"?>

<rdf:RDF
   xmlns:rdf  ="http://www.w3.org/1999/02/22-rdf-syntax-ns#"
   xmlns:rdfs ="http://www.w3.org/2000/01/rdf-schema#"
   xmlns:owl  ="http://www.w3.org/2002/07/owl#"
   xmlns:dc   ="http://purl.org/dc/elements/1.1/"
   xmlns:dct  ="http://purl.org/dc/terms/"
   xmlns:xsd  ="http://www.w3.org/2001/XMLSchema#"
   xmlns:foaf ="http://xmlns.com/foaf/0.1/">

   <rdf:Description rdf:about="http://example.com/aReallyGreatBook">
      <dc:title>A Really Great Book</dc:title>
      <dc:publisher>Examples-R-Us</dc:publisher>
      <dc:creator>
         <rdf:Description>
            <foaf:mbox>john@example.com</foaf:mbox>
         </rdf:Description>
      </dc:creator>
      <dc:contributor>
         <rdf:Description>
            <rdf:type rdf:resource="http://xmlns.com/foaf/0.1/Person"/>
            <foaf:name>Jane Doe</foaf:name>
         </rdf:Description>
      </dc:contributor>
      <dc:language>en</dc:language>
      <dc:format>application/pdf</dc:format>
      <dc:rights>Copyright (C) 2004 Examples-R-Us. All rights reserved.</dc:rights>
      <dct:issued rdf:datatype="http://www.w3.org/2001/XMLSchema#date">2004-01-19</dct:issued>
      <rdfs:seeAlso rdf:resource="http://example.com/anotherGreatBook"/>
   </rdf:Description>

   <rdf:Statement>
      <rdf:subject rdf:resource="http://example.com/aReallyGreatBook"/>
      <rdf:predicate rdf:resource="http://purl.org/dc/elements/1.1/format"/> 
      <rdf:object>application/pdf</rdf:object>
      <rdfs:isDefinedBy rdf:resource="http://example.com/book-formats.rdf"/>
   </rdf:Statement>

</rdf:RDF>

References

[1] W3C Semantic Web Activity http://www.w3.org/2001/sw/

[2] URIQA http://sw.nokia.com/uriqa/URIQA.html

[3] RDF http://www.w3.org/RDF/

[4] RFC2616 - HTTP 1.1 http://www.ietf.org/rfc/rfc2616.txt

[5] Architecture of the WWW http://www.w3.org/TR/webarch/

[6] OWL http://www.w3.org/2004/OWL/

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