Understanding RDF

John Cowan cowan at locke.ccil.org
Mon Jan 25 20:18:43 GMT 1999

Paul Prescod wrote:

> > And here's my attempt to make unabbreviated correct RDF:
>                 ^^^^^^^
> This fills me with a grave sense that RDF should not be going to PR. Few
> people seem confident of their understanding and the first major use is
> already asking for an extension!

Ah, but I have two problems: I need to generate correct unabbreviated
RDF that *has the same meaning* as the given DCD.  I have every confidence
in my ability to generate correct unabbreviated (or abbreviated) RDF
on a subject of my own devising.  Doing it from the rather poorly
specified DCD vocabulary is another matter.

It is one thing to write in a (natural) language, quite another to
translate another's work into that language with confidence.

> You've obviously gone to a lot of work so I'm reluctant to ask you to
> defend your expansion in terms of the two specifications, but my question
> is whether you think that it is possible. Are the two specs unambiguous
> enough that your expansion is something that a generic RDF processor could
> achieve.

Provided it understood the slightly deviant RDF (with no RDF:li
elements) that DCD uses.

> For example:
> >     <Group>
> >      <Element>LastName</Element> <Element>FirstInitial</Element>
> >      <Element>SeatRow</Element> <Element>SeatLetter</Element>
> >      <Element>Departure</Element> <Element>Class</Element>
> >     </Group>
> Did you decline to expand that? Or is that the expansion?

Mm, some of each.  The RDF Syntax and Schema documents, read together,
tell us that RDF schemas can define new kinds of sequence containers
by making RDF statements saying that the new container type is a
subclass of RDF:Seq.

Strictly speaking, that statement is part of a meta-DCD rather 
than of a DCD instance (part of the meta-meta-document).

> Should I
> interpret Group as an RDF Seq? The "RDF:Order='Seq'" is confusing because
> I think that it applies to instances described by the DCD, and not to the
> DCD document itself.

Yes, I omitted that attribute in error.  It should not belong to the
RDF namespace, of course.  Group is a subclass of RDF:Seq, but that
has nothing to do with the ordering it is *modeling*.

> > <RDF:Description>
> >  <RDF:type resource="http://w3.org/TR/1998/NOTE-dcd-19980731#DCD"/>
> >   <RDF:li>
> >    <RDF:Description>
> It isn't clear to me how the RDF:li can go right in an RDF:Description.
> Where is the containing rdf:Seq, rdf:Bag and rdf:Alt? What abbreviation is
> this?

Oops.  Chalk it up to defective translation.  But that was a mechanical
error, not a defect in RDF itself.  (I caught another such error,
failing to use the "resource" attribute, before I posted; I can't
catch everything.)
John Cowan	http://www.ccil.org/~cowan		cowan at ccil.org
	You tollerday donsk?  N.  You tolkatiff scowegian?  Nn.
	You spigotty anglease?  Nnn.  You phonio saxo?  Nnnn.
		Clear all so!  'Tis a Jute.... (Finnegans Wake 16.5)

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