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SOURCE : handling a graph read in twice at different times

From: Seaborne, Andy <andy.seaborne@hp.com>
Date: Sat, 15 Jan 2005 20:37:57 +0000
Message-ID: <41E97F25.5060702@hp.com>
To: Steve Harris <S.W.Harris@ecs.soton.ac.uk>
Cc: RDF Data Access Working Group <public-rdf-dawg@w3.org>

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.

Recreating #source-query-001 as a test:

Using urn:'s for the internal names so it is clear what's internal and 
what's the web URI.

=================================
# Graph: <http://example.org/foaf/graph>
# Read in and stored as <urn:x-local:graph1>

@prefix  foaf:  <http://xmlns.com/foaf/0.1/> .

_:a  foaf:name     "Alice" .
_:a  foaf:mbox     <mailto:alice@work.example> .

_:b  foaf:name     "Bob" .
_:b  foaf:mbox     <mailto:bob@oldcorp.example.org> .

=================================
# Graph: <http://example.org/foaf/graph>
# Read in and stored as <urn:x-local:graph2>

@prefix  foaf:  <http://xmlns.com/foaf/0.1/> .

_:a  foaf:name     "Alice" .
_:a  foaf:mbox     <mailto:alice@work.example> .

_:b  foaf:name     "BOB" .
_:b  foaf:mbox     <mailto:bob@newcorp.example.org> .

=================================

Read from same URI - different contents

=================================
# Provenance information:
# Default graph
@prefix dc:  <http://purl.org/dc/elements/1.1/> .
@prefix xsd:        <http://www.w3.org/2001/XMLSchema#> .

<urn:x-local:graph1>   dc:source      <http://example.org/foaf/graph> .
<urn:x-local:graph1>   dc:date        "2004-12-06"^^xsd:date .

<urn:x-local:graph2>   dc:source      <http://example.org/foaf/graph> .
<urn:x-local:graph2>   dc:date        "2005-01-10"^^xsd:date .

=================================


==== 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 |
----------------------------------------------------------------------

then

==== 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> |
---------------------------------------------

These put the provenance informatin in the unnamed graph but it could be 
placed in different named graph:

==== Query 3 :
# Provence information in another named graph
PREFIX foaf: <http://xmlns.com/foaf/0.1/>
PREFIX dc: <http://purl.org/dc/elements/1.1/>

SELECT DISTINCT ?name ?source

GRAPH <urn:x-local:details>
GRAPH <urn:x-local:graph1>
GRAPH <urn:x-local:graph2>

WHERE SOURCE ?snode (?person foaf:name ?name)
       SOURCE ?prov  (?snode dc:source ?source)
       SOURCE ?prov  (?snode dc:date   ?date)

results same as query 2:

---------------------------------------------
| name    | source                          |
=============================================
| "Alice" | <http://example.org/foaf/graph> |
| "BOB"   | <http://example.org/foaf/graph> |
| "Bob"   | <http://example.org/foaf/graph> |
---------------------------------------------

Query 3 shows that a system can manage different sets of assertions about 
named graphs at the same time.

	Andy
Received on Saturday, 15 January 2005 20:38:34 GMT

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