W3C Toward Swell

Toward Swell, the Semantic Web Logic Language

status: originally sketched just before a 6 Jul meeting; integrating into more swell stuff before a 19-20 July meeting
Dan Connolly
$Revision: 1.15 $ of $Date: 2000/07/27 00:52:57 $ by $Author: connolly $
  1. the basic RDF statement model: subject, predicate, and object

    see also: this section of a swell paper

  2. Schema/Ontology basics: Classes, properties
  3. propositional calculus: introducing implies, false
  4. predicate calculus: introducing forall (and in doing so, variables)
  5. Future work:

An Introduction to the Resource Description Framework (RDF)

Introduction

taken from Some "What is RDF" bits Lynn Stein (Mon, Jul 03 2000)

Most knowledge representations share a common structure. Semantic networks[Woods], hypertext[Drakos], etc. use a a directed, labelled graph structure where nodes represent objects and the arcs that connect them represent assertions *note. In frame-based representations [Minsky], slot-relations connect role-fillers to a frame; frames themselves may also be interconnected by relations such as inheritance. In logical formalisms[McCarthy], binary relations are easily expressed using this property notation, though arbitrary n-ary relations require an additional translation mechanism *note.

The Resource Description Framework [RDF] is an emerging standard for the exchange of knowledge in the form of directed, labelled graphs. At its core is this notion of a statement, with a subject and an object related by a property. For example

Dan is the author of the program.

"Dan" is the source, or the subject, of the statement, "is the author of" is the property, and "the program" is the object.

RDF builds on commodity web technologies: Uniform Resource Identifiers[URI] for identifier syntax, and Extensible Markup Language[XML] for structured syntax. Each of the subject, object, or property in an RDF statement can be a URI. The core of the XML syntax for RDF does little more than distinguish the parts of a statement. So, to persue the example above, we might represent that statement as:

<rdf:RDF
  xmlns:rdf="http://www.w3.org/1999/02/22-rdf-ns#"
  xmlns:dublinCore="http://purl.org/dc/elements/1.0/">



  <rdf:Description about="#theProgram">
     <dublinCore:creator>Dan Connolly</dublinCore:creator>
  </rdf:Description>



</rdf:RDF>

where dublinCore is the namespace for the Dublin Core metadata @@ (explain XML namespaces in a sentence or two).

@@@Dan stopped here.

If this description now exists in some document, it can be given a URI. @@@ establish example.

Then we can say

subject

predicate

object

The subject and object can be any resource. But the predicate must be a property @@@

Stuff on typing, restrictions (domain, range), class, subclass, subproperty.

Need containers, comments, labels, ...?

Also pictures throughout (that someone else gets to draw).

Footnotes

  1. Note that this does not preclude the inclusion of arcs as "objects" connected by other arcs.
  2. Either of two alternatives techniques can be used to express n-ary relations using binary properties: currying or reification.

References

[Rao & Turoff]
Rao, Usha & Turoff, Murray. Hypertext Functionality: A Theoretical Framework, International Journal of Human-Computer Interaction, 1990.
[Craw90]
Crawford, J. (1990), Access-Limited Logic: A Language for Knowledge Representation, Doctoral dissertation, Department of Computer Sciences, University of Texas at Austin, Austin, Texas. UT Artificial Intelligence TR AI90-141, October 1990. (Algernon and Access-Limited Logic)
[RDF]
Lassila, Swick [eds], Resource Description Framework (RDF) Model and Syntax Specification (World Wide Web Consortium Recommendation, 1999)
http://www.w3.org/TR/1999/REC-rdf-syntax-19990222
[URI]
August 1998 Uniform Resource Identifiers (URI): Generic Syntax
(RFC 2396) T. Berners-Lee, R. Fielding, L. Masinter
[XML]
Feb 1998: W3C Recommendation: Extensible Markup Language (XML) 1.0

Acknowledgements and @@Fodder