- From: Jonathan Borden <jonathan@openhealth.org>
- Date: Fri, 20 Sep 2002 17:33:18 -0400
- To: "Tim Bray" <tbray@textuality.com>, <www-tag@w3.org>
Tim Bray wrote: > > The latest draft of RDF Model Theory > (http://www.w3.org/TR/2002/WD-rdf-mt-20020429/) says a couple of > interesting things. > ...> > And in section 1.2 "Urirefs are treated as logical constants, i.e. as > names which denote something (the things are called 'resources', but no > assumptions are made about the nature of resources.)" > Perhaps the most definitive statements are found in: 0.2 Graph syntax (http://www.w3.org/TR/rdf-mt/#graphsyntax) where: [[ To describe RDF graphs it is first necessary to define the things that can act as nodes and arcs of the graph. There are three kinds of node in any RDF graph: urirefs, literals, and blank nodes. A uriref is defined to be a URI reference in the sense of [RFC 2396]. An RDF literal has three parts ( a bit, a character string, and a language tag), but we will treat them simply as character strings, since the other parts of the literal play no role in the model theory. Blank (unlabeled) nodes are considered to be drawn from some set of 'anonymous' entities which have no label and are unique to the graph. Finally, every arc in an RDF graph is labelled with a uriref. The same uriref may label several arcs and also be a node in the graph. An RDF graph can then be defined as a set of triples of the form <S, P, O>, where P is a uriref, S is either a uriref or a blank node, and O is either a uriref, a blank node, or a literal. It is convenient to adopt a familiar abuse of terminology and identify a single triple with the graph consisting of the singleton set containing that triple. We refer to urirefs and literals (but not blank nodes) as names; but note that there is no distinction between the name of a node and the node itself. A name may occur in more than one graph, but blank nodes are unique to each graph. This reflects the fact that literals always have the same meaning and urirefs are considered to have a 'global' meaning but blank nodes do not. (Note that this is a simplification from earlier versions, which distinguished between literals and literal nodes.) ]] In particular: _note that there is no distinction between the name of a node and the node itself_ In terms of a URIref, if there is no distinction between the name (the URIref) and the node (i.e. the resource) then the two are said to have _identity_. Jonathan
Received on Friday, 20 September 2002 17:50:58 UTC