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Re: Question/Comment on FROM and WITH

From: Seaborne, Andy <andy.seaborne@hp.com>
Date: Wed, 23 Feb 2005 14:58:53 +0000
Message-ID: <421C9A2D.4000403@hp.com>
To: Geoff Chappell <geoff@sover.net>
Cc: public-rdf-dawg-comments@w3.org

Geoff Chappell wrote:
> Are graph labels lost when assembling a background graph with WITH clause?

Yes, they are.

> E.g. what would I get for this query?
 >
> 
> SELECT ?src
> WITH <http://example.org/foaf/aliceFoaf> <http://example.org/foaf/bobFoaf> 
> WHERE
>   GRAPH ?src
>   {
>     ( ?x ?y ?z )
>   }
> 
> and what about this one - will it return any results?
> 
> SELECT ?x
> FROM <http://example.org/foaf/aliceFoaf> 
> WHERE
>     ( ?x ?y ?z )

There are no solutions to either query.  And, yes, it's potentially confusing.
As in the message to Bob MacGregor, suggestions for better names most welcome -
to date other suggestions tend to have biases in one direction or another,
depending on the suggesters view of usage.

> If the graph labels are maintained, I see no distinction between FROM and
> WITH. If they're not, then example queries such as in 8.1 and 8.2 are pretty
> confusing and I'd suggest using explicit FROM/WITH.

I see if adding an explicit dessciption of the datasets used in section 8 helps.

At one time, the document had the discussion of WITH/FROM before GRAPH (what is 
now sec 8)  so that the reader can see the important concept of RDF dataset and
how to access it, before WITH/FROM which are just one way a dataset to given to
a query execution.  I don't expect WITH/FROM to be the usual way for systems to
get of any size where I expect the dataset to be passed to the query engine
programmaticaly if it isn't implicit by choice of query engine anyway.

We did discuss the fact that association of the dataset to the query execution
is a protocol issue, but sometimes there is no "protocol" to perform this (e.g.
local query).


> 
> Geoff

	Thanks for the comments,
	Andy
Received on Wednesday, 23 February 2005 15:33:18 GMT

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