- From: Alberto Reggiori <alberto@asemantics.com>
- Date: Tue, 1 Jun 2004 18:32:40 +0200
- To: Steve Harris <S.W.Harris@ecs.soton.ac.uk>
- Cc: public-rdf-dawg@w3.org
On Jun 1, 2004, at 6:01 PM, Steve Harris wrote:
>
> On Tue, Jun 01, 2004 at 11:23:51 +0900, Eric Prud'hommeaux wrote:
>> rdql- : 4.2 Provenance
>
> True, but several (3+) of the implementations have added a 4th member
> to
> the pattern, eg:
>
> SELECT ?vcard, ?source
> WHERE (?vcard vcard:FN "John Smith" ?source)
>
> will tell you the "source" of the statement.
+1
4th component into triple-pattern would basically allow the user to
refer/pin-point and extract graph specific information (source,
provenance, context) - the graph itself could be seen as a resource
(and then further described), and the graph-name could either be a URI
qualified resource or bNode (typedNode perhaps). Such scenario turned
out to be quite common (and realistic) as soon as one starts to query
heterogeneous RDF federations (e.g. crawled overlapping RDF statements)
For another practical use-case of more than 3 components
triple-patterns in RDQL-like syntax see recent "Named Graphs" work
[1][2][3] - which seems somehow motivating this. Where in the published
papers/posters the syntax presented looks like the following:
SELECT ?x, ?y
WHERE
?a (?b rdf:type ex:Person .
?b rdf:hasName ?x .
?b ex:homepage ?y)
(?a dc:date ?c)
AND ?c > "1/1/2003"
'?a' would be the graph-name I guess
Annotea work seems also motivating this requirement - and implemented
in Algae (EricP?) - I guess Steve (us and others out there) got some
other real-world use-cases for this, if somebody is interested.
and yes - it is very useful - even if still outside from the DAWG
"radar" unfortunately :)
Yours
Alberto
[1] http://www.w3.org/2004/03/trix/
[2] http://www.wiwiss.fu-berlin.de/suhl/bizer/SWTSGuide/p747-bizer.pdf
[3]
http://lists.w3.org/Archives/Public/www-archive/2004Feb/att-0072/swig-
bizer-carroll.pdf
Received on Tuesday, 1 June 2004 12:32:55 UTC