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Re: SOURCE : handling a graph read in twice at different times

From: Steve Harris <S.W.Harris@ecs.soton.ac.uk>
Date: Sun, 16 Jan 2005 03:18:15 +0000
To: RDF Data Access Working Group <public-rdf-dawg@w3.org>
Message-ID: <20050116031814.GA14178@login.ecs.soton.ac.uk>

On Sat, Jan 15, 2005 at 08:37:57 +0000, Andy Seaborne wrote:
> Steve Harris wrote:
> >On Fri, Jan 14, 2005 at 03:38:01PM -0600, Dan Connolly wrote:
> >
> >>If you have a novel position on an issue, not represented by one of the
> >>options or even close, mail the wg with the issue name in the subject
> >>and I'll try to add it.
> >
> >
> >For the SOURCE issue I would like what Alberto and I do currently to be
> >considered, as in
> >http://www.w3.org/2001/sw/DataAccess/tests/#source-query-001 2 3 & 5
> >AFAIK it is the only solution that was arrived at independently by more
> >than one working group member, and it represents our development and
> >support experience.
> >
> >The key feature is that the URI used to identify the triples (ie. bound by
> >the SOURCE keyword) is not neccesarily the URI that was resolve to
> >retreive the grpah, that may be got by following some predicate from the
> >SOURCE URI to the actual URI resolved (dc:sounrce in the testcases).
> >
> >This allows more that one version of a graph identified by the same URI to
> >be present in the store at one time, without confusion.
> >
> >- Steve
> >
> 
> This is possible with the mechanism currently in the document.
> 
> rq23 does not prescribe that the URI that names the graph is the URI it is 
> read from and a predicate can connect the two - it's your choice  Use of 
> FROM or GRAPH is optional - the RDF dataset can be set externally but I 
> have used them here so that the queries can go in a manifest.

OK, that sounds good.
 
> ==== Query 1 :
> 
> PREFIX foaf: <http://xmlns.com/foaf/0.1/>
> PREFIX dc: <http://purl.org/dc/elements/1.1/>
> 
> SELECT DISTINCT ?name ?source ?date
> 
> # explicitly name the graphs just for clarity - note internal names
> # Manifest format can't express this externally.
> 
> FROM  <urn:x-local:details> # The place when provenance info is kept
> GRAPH <urn:x-local:graph1>  # Allocated when aliceFoaf read in
> GRAPH <urn:x-local:graph2>  # Allocated when bobFoaf   read in
> 
> WHERE SOURCE ?snode (?person foaf:name ?name)
>       (?snode dc:source ?source)
>       (?snode dc:date   ?date)
> 
> and I get:
> 
> ----------------------------------------------------------------------
> | name    | source                          | date                   |
> ======================================================================
> | "Alice" | <http://example.org/foaf/graph> | "2005-01-10"^^xsd:date |
> | "BOB"   | <http://example.org/foaf/graph> | "2005-01-10"^^xsd:date |
> | "Bob"   | <http://example.org/foaf/graph> | "2004-12-06"^^xsd:date |
> | "Alice" | <http://example.org/foaf/graph> | "2004-12-06"^^xsd:date |
> ----------------------------------------------------------------------

Great, but whats the purpose of the FROM and GRAPH keywords here? Are they
to illustrate something I'm missing, or are they neccesary?
 
> ==== Query 2 :
> PREFIX foaf: <http://xmlns.com/foaf/0.1/>
> PREFIX dc: <http://purl.org/dc/elements/1.1/>
> 
> SELECT DISTINCT ?name ?source
> 
> FROM  <urn:x-local:details>
> GRAPH <urn:x-local:graph1>
> GRAPH <urn:x-local:graph2>
> 
> WHERE SOURCE ?snode (?person foaf:name ?name)
>       (?snode dc:source ?source)
>       (?snode dc:date   ?date)
> 
> ---------------------------------------------
> | name    | source                          |
> =============================================
> | "BOB"   | <http://example.org/foaf/graph> |
> | "Alice" | <http://example.org/foaf/graph> |
> | "Bob"   | <http://example.org/foaf/graph> |
> ---------------------------------------------

Ditto.

Also, if you read in a graph that has:

<owl:Ontology rdf:about="">
  ...
</owl:Ontology>

Does the ... get assertad with urn:x-local:foo, or the resolved URI as its
subject?

- Steve
Received on Sunday, 16 January 2005 03:18:20 GMT

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