- From: Peter F. Patel-Schneider <pfpschneider@gmail.com>
- Date: Wed, 13 Jul 2016 09:00:02 -0700
- To: james anderson <james@dydra.com>, public-sparql-exists@w3.org
On 07/13/2016 08:56 AM, james anderson wrote:
> good afternoon;
>
>> On 2016-07-13, at 16:52, Peter F. Patel-Schneider <pfpschneider@gmail.com
>> <mailto:pfpschneider@gmail.com>> wrote:
>>
>> […]
>> I do believe that it is useful to put this sort of information into an area
>> that can be easily edited by group members. The W3C wikis appear to me to be
>> a good candidate for this purpose - can this group get one? If not, maybe the
>> github wiki can be used, but not with a fixed format per issue.
>
> in order for any discussion to proceed, the topic statement snneds to include
> all of the things which are in that table.
> if the do not appear in a table, but rahter in a description list it reall
> does not matter.
> they just all need to be in one place.
>
> best regards, from berlin,
> ---
> james anderson | james@dydra.com <mailto:james@dydra.com> | http://dydra.com
Why does
*****
Problem 1: Some uses of EXISTS are not defined during evaluation
The evalution of exists in 18.6 is only defined for graph patterns, but in
SELECT ?x WHERE {
?x :p :c .
FILTER EXISTS { SELECT ?y { ?y :q :c . } } }
the argument to exists ends up being a ToMultiSet, which is not listed under
"Graph Pattern" in the table of SPARQL algebra symbols in 18.2.
The argument to exists is not explicitly listed as a "Graph Pattern" when
the argument to EXISTS is a GroupGraphPattern containing just a SubQuery or
just an InlineData. Here the join is simplified away by section 18.2.2.8
leaving a construct in the SPARQL algebra that is not listed as a graph
pattern symbol, ToMultiSet or a multiset, respectively. An example of where
this happens (but not at the top level of an EXISTS) is the last example of
18.2.3.
*****
need any dataset or intended solution for discussion to proceed? Why does it
even need "the pertinent query"?
Examples can be useful to help push a discussion but a complete example is not
necessary for this purpose.
peter
Received on Wednesday, 13 July 2016 16:00:34 UTC