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Re: ACTION: a replacement for 4.5 focussed on union query

From: Dan Connolly <connolly@w3.org>
Date: Tue, 27 Jul 2004 09:32:10 -0500
To: Simon Raboczi <raboczi@tucanatech.com>
Cc: RDF Data Access Working Group <public-rdf-dawg@w3.org>
Message-Id: <1090938730.314.692.camel@dirk>

On Tue, 2004-07-27 at 05:22, Simon Raboczi wrote:
> The current (CVS revision 1.128) text is
> [[
> 4.5 Aggregate Query
> It should be possible to specify two or more RDF graphs against which a  
>   query shall be executed; that is, the result of an aggregate query is  
> the  merge of the results of executing the query on each of two or more  
>   graphs.
> ]]
> Previous discussion about "aggregate query" versus "union query"  
> occurred in a thread starting from [1].
> We can build on top of the "merge" defined in RDF Semantics[2], and the  
> guarantee that "a set of graphs can be treated as equivalent to its   
> merge, i.e. a single graph, as far as the model theory is concerned."   
> I suggest text as follows:
> [[
> 4.5 Querying multiple sources
> It should be possible for a query to specify which of the available RDF  
> graphs it is to be executed against.  If more than one RDF graph is  
> specified, the result is as if the query had been executed against the  
> merge[3] of the specified RDF graphs.
> ]]
> Processors with a single available RDF graph should trivially satisfy  
> this objective.

I'd prefer to note that in the document. And I'd like a short
discussion of the down-side of this feature. Perhaps:

  ... specified RDF graphs.

  Some services only offer to query one graph; they are considered
  to trivially satisfy this objective.

  While a variety of use cases motivate this feature, it is not
  a requirement because it is not
  clear whether this feature can be implemented in a generally
  scalable fashion.

> [1]  
> http://lists.w3.org/Archives/Public/public-rdf-dawg/2004AprJun/
> 0777.html
> [2] http://www.w3.org/TR/rdf-mt/
> [3] http://www.w3.org/TR/rdf-mt/#graphdefs
Dan Connolly, W3C http://www.w3.org/People/Connolly/
Received on Tuesday, 27 July 2004 10:31:55 UTC

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