graph terminology (was Re: Comments on "SPARQL 1.1 Uniform HTTP Protocol for Managing RDF Graphs")

This is a personal response, not on behalf of any Working Group.  I
removed from the CC line, because I'm
not actually commenting on that document.

On Fri, 2011-03-18 at 13:43 +0100, Kjetil Kjernsmo wrote:
> Hi all!
> I have previously complained that the "Dataset HTTP Protocol" specification is 
> difficult to understand and possibly in conflict with webarch, and I've been 
> challenged to be more specific. Now, I've tried to see the issue from more 
> sides, and I found an old post from timbl that pinpoints a key issue, and for 
> that reason, I have chosen to follow up on that post instead of starting a 
> new thread.
> Tim Berners-Lee wrote a long time ago:
> > 4) So when a GET or PUT is done, this is an implementation of HTTP. It is
> > not a new protocol, in that HTTP only is used.  You can't know AND SHOULD
> > NOT BE ABLE TO KNOW that in fact there is a SPARQL engine behind it.  That
> > bit in caps as it is essential when you provide HTTP that you do totally
> > support HTTP, so everything like creation date and expiry etc etc all hold.
> > You may well use conneg as well for PUT and GET, for example.  Where GET
> > and PUT are concerned this is not a new protocol, and the document should
> > take the position as to it is explaining how for a SPARQL service owner to
> > support HTTP on those graphs (or rather, virtual RDF documents).
> So, the key issue and the root of my confusion is the question: "What does the 
> URI of a information resource consisting of some RDF triples identify?" The 
> question isn't admittedly not very precise, for a reason that will be 
> apparent soon. 

It's a "g-box".

That's a new term we've started using in the RDF Working Group, trying
to sort out this kind of confusion.    Hopefully we'll come up with a
better term for long-term use, but this seems good enough for now.

For more details, see the proposal:
or the wiki page about it, with a diagram:

> Lets take an example: What does the URI 
> identify? Apart from a foaf:PersonalProfileDocument, is it an RDF Graph or an 
> RDF Document? 
> For reference, "RDF graph" was originally defined in Concepts and Abstract 
> Syntax AFAICS:
> whereas "RDF Document" was defined in RDF/XML Syntax:
> My intuition has always been that 
> identifies an RDF Document, and this intuition seems to be shared by at least 
> the "Cool URIs for the Semantic Web" Note:
> While this is just a Note, and may not even use the term in the meaning of 
> RDF/XML Syntax specification.
> It is then my interpretation of timbl's post above that if 
> identifies an RDF Document and not an RDF 
> Graph, then, if that document happens to be served by a SPARQL RDF Dataset 
> protocol server rather than from a file on a filesystem on an Apache server 
> as today, this MUST NOT change, if the specification insists on a 200 
> response (which it should, IMHO).
> So, my issue all boils down to whether the URI of the stuff that people have 
> been publishing for years identifies RDF Documents or RDF Graphs. If it 
> identifies an RDF Graph, then the current spec is OK (if still somewhat 
> opaque), but if it identifies an RDF Document, there surely is an 
> inconsistency somewhere?
> Surely, a resource can't be both an RDF Document and an RDF Graph? Further, 
> does it have any bearing on the problem that 
> is a foaf:PersonalProfileDocument? Can 
> something be both a foaf:PersonalProfileDocument and an RDF Document? (my 
> intuition says yes) Can something be both a foaf:PersonalProfileDocument and 
> an RDF Graph? (my intuition says no). There are many other conventional 
> resources to identify the same way, owl:Ontology and cc:Work comes to mind. 
> Would the answer be any different? 
> Now, I've possibly exposed myself as totally confused about core Semantic Web 
> concepts, but I do so with the confidence that I'm not a n00b, and if I'm 
> confused, I'm probably not alone, and the issue should be properly explained 
> to the community.

You're hardly the first person to wade into this swamp.  :-)   Most of
the time we do it, we just make it muddier.  Hopefully these new terms
give us some more solid footing.

I'm not the best person to respond to your specific comments about the
document, so I'll let others do that.

    -- Sandro

Received on Friday, 18 March 2011 13:53:37 UTC