RDF *already* supports literal subjects - a thought experiment

It has already been suggested that data: URIs provide a way to implement
subjects-as-literals in RDF.  I thought it might be worth fleshing this out a
little to see where it leads...


A data: URI (http://tools.ietf.org/html/rfc2397) has the following general form:


For representing literals (which are, after all, sequences of characters), we
can probably disregard the [;base64] option.

To distinguish data: as literals, I would suggest introducing a new MIME type, say:

   application/rdf-literal [;datatype=uri] [;language=<lang-code>]

where datatype= indicates a typed literal, and language may be present for
non-typed literals.

(%-escaping would be applied as necessary for the data: URI to conform to URI 
syntax.  I won't worry with the details in this message.)

Thus, we can have:


intended to denote the same thing in RDF as the plain literal "Hello world", or:


to denote the same as "Bonjour monde"@fr (using Turtle notation here for the
literal), or:


to denote the same as "10"^^<http://www.w3.org/2001/XMLSchema#integer>, or the
integer 10.


So far, all this should lead to intended-literals in subject position that can
be read by any existing RDF/XML consuming application.

What I'm less sure about is fixing the semantics:  as it stands, the RDF
semantics is expressed in terms of allowing arbitrary interpretations --
mappings to things in the domain of discourse -- for all URI nodes in a graph.
Would it be unreasonable or problematic to say that, for this particular form of
URI, the  denotation is fixed by the same general rules that govern the
denotation of literals?


A side effect of this approach might be that if a web server were to dereference
a URI to a value returned with MIME type application/rdf-literal, then for
overall consistency that would constrain the semantics of the URI used to
access such a resource (subject to the usual caveats about not everything
in the web being a truth).


I think an approach like this maybe could avoid the objections vis-a-vis 
deployment economics to allowing literal subjects, and leave a path clear for 
some future development (e.g. N3 based) that allows literals more directly.


Received on Friday, 9 July 2010 17:56:10 UTC