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Re: Questions and comments on SPARQL 1.1 Graph Store HTTP Protocol draft

From: Sandro Hawke <sandro@w3.org>
Date: Sat, 24 Dec 2011 08:14:15 -0500
To: Andy Seaborne <andy.seaborne@epimorphics.com>
Cc: SPARQL Working Group <public-rdf-dawg@w3.org>
Message-ID: <1324732455.2202.73.camel@waldron>
On Thu, 2011-12-22 at 16:44 +0000, Andy Seaborne wrote:
> Re-directed to the working group list.
> 
> On 22/12/11 16:01, Sandro Hawke wrote:
> >>> One convention we have adopted is to use the null relative URL (<>  in
> >>> Turtle, or "" in RDF/XML). I'd like to know whether there is a standard
> >>> way of doing this. Maybe the spec should indicate one.
> >>>
> >>
> >>
> >> This would require a base URI resolution mechanism that would (in the end) simply resolve this to the request-URI (per base URI resolution rules). The WG has decided to not support a base URI resolution mechanism for this specification. So, without a discovery mechanism the only way to perform this "append" behavior is to know the URI of the Graph Store before hand and to POST to it directly.
> >
> > So the suggested workaround is to POST to the graphstore to get a new
> > URL allocated, then PUT your graph to that new address.   And your
> > understanding is that the technique Arnaud is suggesting -- defining the
> > base URI as the URI that is allocated to hold the content -- could be
> > standardized in the future?
> 
> Sandro,
> 
> By your reading, does RFC 3986 "5.1.  Establishing a Base URI" and RFC 
> 2616 defining a request URI apply here?
> 
> If so, doesn't that say what the base URI is?
> If not, why don't these RFCs apply?

Sorry, I know you asked this earlier, and in the crush of events I lost
track of it.

As I read RFC 3986 section 5.1, it doesn't constrain the base URI for
the content of a POST.  So it falls back to the outer-ring, in that
diagram, of being application dependent.  That seems right to me -- in
this case, the application is whichever POST semantics the given
resource implements.  For POSTing to the graphstore itself (but not the
elements inside it), I believe we can specify the protocol for POST, and
saying how it handles relative URIs in RDF syntaxes seems to me like a
reasonable part of that.

I don't see anything in 2616 that directly bears on this; perhaps I'm
missing something.

The biggest stretch, I think, is how to talk about what is being
serialized in a POST.   Strictly speaking, it's not an RDF graph, since
it has relative URIs.  Logically, it's some kind of "relative RDF
graph", but that's not in the current RDF specs.   My sense is that
while it's not perfect, it would be acceptable for whatever spec says
this relative-URIs-in-POSTing is okay to also define this variation on
RDF graphs.

An alternative would be to define some well-known URI to use as the base
(eg "http://www.w3.org/2011/move-during-post/"), and the POST-handler
can rewrite those absolute URIs to new URIs.  But to me that seems less
attractive than just using relative URIs.

    -- Sandro



> 	Andy
> 
> 
Received on Saturday, 24 December 2011 13:14:25 GMT

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