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FROM and FROM NAMED: To fetch or not to fetch?

From: David Booth <david@dbooth.org>
Date: Sat, 02 Jun 2012 23:42:22 -0400
To: public-rdf-dawg-comments <public-rdf-dawg-comments@w3.org>
Message-ID: <1338694942.18938.6708.camel@dbooth-laptop>
When a SPARQL query is issued to a server using the FROM <U> (or FROM
NAMED <U>) syntax, is the server supposed to fetch that graph from U or
is it supposed to only look among its existing named graphs for U?

Sec 13.2 says:
http://www.w3.org/TR/sparql11-query/#specifyingDataset
[[
The FROM and FROM NAMED keywords allow a query to specify an RDF dataset
by reference; they indicate that the dataset should include graphs that
are obtained from representations of the resources identified by the
given IRIs (i.e. the absolute form of the given IRI references).
]]

And sec 13.2.2 further says:
http://www.w3.org/TR/sparql11-query/#namedGraphs
[[
The FROM NAMED syntax suggests that the IRI identifies the corresponding
graph, but the relationship between an IRI and a graph in an RDF dataset
is indirect.
]]

These sections certainly make it sound like the server is supposed to
fetch from the URI (or perhaps use a cached version if it is fresh).
But I just tried this with three different SPARQL servers, and only one
fetches from the URI.  The others only look among their existing named
graphs.

There is a big difference between fetching and not fetching.  As a query
writer I need to know which behavior is correct.  

Personally, although the fetching behavior seems convenient for some
things, I think the non-fetching behavior seems more sensible, because: 

1. If the correct behavior were to not fetch, then named graphs could be
fetched using LOAD INTO GRAPH anyway.

2. If the correct behavior were to fetch then I don't know how one would
specify multiple already-loaded named graphs to be used as the default
graph in a query.

3. If the spec is intentionally ambiguous about fetching or not fetching
then that would be a problem, because I certainly would not want a
server trying to fetch without my control.

Clarification please?

Thanks



-- 
David Booth, Ph.D.
http://dbooth.org/

Opinions expressed herein are those of the author and do not necessarily
reflect those of his employer.
Received on Sunday, 3 June 2012 03:42:55 GMT

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