- From: Jeen Broekstra <jeen@aduna.biz>
- Date: Fri, 10 Jun 2005 10:36:45 +0200
- To: Dan Connolly <connolly@w3.org>
- Cc: RDF Data Access Working Group <public-rdf-dawg@w3.org>
Dan Connolly wrote:
> On Thu, 2005-06-09 at 14:54 +0200, Jeen Broekstra wrote:
[snip]
>>Suggested definitions:
>>
>> Definition: *Basic Graph Pattern*
>>
>> A /basic graph pattern/ is a set of Triple Patterns.
>>
>> Definition: *Graph Pattern Match*
>>
>> A graph pattern /matches/ on a graph G with pattern solution S iff
>> S(GP) is a non-empty subgraph of G.
>
>
> Yes, but... why non-empty? Consider:
>
> SELECT * where {}.
>
> In the case of the empty solution (i.e. empty set of bindings),
> S(GP) is just GP, which is empty. We want that to be a match,
> right? i.e. ASK where {} always gives yes, right?
To clarify: I included the non-empty bit because I thought it would
otherwise regress to the empty set being a valid match for _any_ graph
pattern.
I just had a look again however, and this is not the case. (My error
was that I thought S might map to an empty set; I'd misread something
in the definition of the mapping. Mea culpa).
Jeen
--
Jeen Broekstra Aduna BV
Knowledge Engineer Julianaplein 14b, 3817 CS Amersfoort
http://aduna.biz The Netherlands
tel. +31 33 46599877
Received on Friday, 10 June 2005 08:38:02 UTC