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Re: Updated definitions (dataset, FROM/FROM NAMED)

From: Dan Connolly <connolly@w3.org>
Date: Thu, 19 May 2005 13:36:22 -0500
To: andy.seaborne@hp.com
Cc: www-archive@w3.org, Pat Hayes <phayes@ihmc.us>, Eric Prud'hommeaux <eric@w3.org>
Message-Id: <1116527782.3429.203.camel@localhost>

On Thu, 2005-05-19 at 11:43 +0100, Seaborne, Andy wrote:
[...]
> >>Definition: SPARQL Query 
> >>
> >>A SPARQL query is a tuple consisting of a graph pattern, an RDF
> >>dataset description, a number of solution sequence modifiers and a
> >>result form.
> >>
> > 
> > Dataset description? Not just a dataset?
> > hmm. I wonder where that comes in...
> > It doesn't seem to show up anywhere else.
> 
> Could do - the query has dataset, and FROM/FROM NAMED are a description.
> How the description gets turns into the datset for the query is left open.  I 
> want to avoid talking about GET (if http://) or what aggregators might do with URIs.

Hmm... I thought we decided that we shall define this feature w.r.t.
GET... ah... well, we haven't decided, but polls indicate this
is the leading option:

[[
std (3 supporters; one strongly opposed)
        FROM/GRAPH are well-defined instructions that interact with the
        web per URI specs
]]
  -- http://www.w3.org/2001/sw/DataAccess/ftf4.html#item07



> > As I think I suggested earlier, the semantics of FROM and FROM NAMED
> > should be specified by reference to the protocol, not as part of
> > the query language formalism.
> 
> The QL should not depend on the protocol:
> 
> 1/ The QL can be used without the protocol

well, you can't use FROM or FROM NAMED without access to The Web,
i.e. without *some* protocol, right?

> 2/ If the protocol does not specify the dataset, it comes from the query syntax 
> so we end out looping here.

My picture is:
 - the QL spec specifies what a dataset is, and gives the
  semantics of queries w.r.t. datasets

 - the protocol spec says how to obtain a dataset from
   2 lists of URIs, using web protocols and RDF merging

 - the QL spec says "a query using FROM/FROM NAMED
   is just like one without FROM/FROM NAMED, where the
   relevant URIs show up in the default-graph-uri
   and named-graph-uri slots in the protocol"

Yes, it's a rat's-nest of dependencies, but that seems to be
what the WG wants.

I can imagine other ways to do it, but I don't see them concretely.

> > 
> > That reminds me... the protocol spec needs to say how
> > to get from the default-graph-uri and the
> > named-graph-uri's to the corresponding graphs.
> > I'll try to remember to send mail about that separately.

-- 
Dan Connolly, W3C http://www.w3.org/People/Connolly/
D3C2 887B 0F92 6005 C541  0875 0F91 96DE 6E52 C29E
see you at XTech in Amsterdam 24-27 May?
Received on Thursday, 19 May 2005 18:36:52 UTC

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