Re: updated draft

On 04/02/2017 11:01 AM, james anderson wrote:
> good evening;
> 
>> On 2017-04-02, at 19:37, Peter F. Patel-Schneider <pfpschneider@gmail.com> wrote:
>>
>> […]
>>>
>>>>
>>>> So you do not agree, for example, that that it is problematic that according
>>>> to the SPARQL specification that the running the query
>>>>
>>>> SELECT ?x WHERE {
>>>>   ?x :p :d .
>>>>   FILTER EXISTS { ?x :q :b . } }
>>>>
>>>> against the graph
>>>>
>>>> _:c :p :d .
>>>> :e :q :b .
>>>>
>>>> produces a result set containing a query solution that maps ?x to _:c?
>>>>
>>>> peter
>>>
>>> it would be problematic were the recommendation to require an implementation to produce that result.
>>> the recommendation does not require that.
>>> i do understand that various interpretations of the recommendation lead one to believe that it implies that result.
>>> those interpretations are flawed.
>>>
>>> best regards, from berlin,
>>>
>>>
>>>
>>> ---
>>> james anderson | james@dydra.com | http://dydra.com
>>
>> Are you saying that the SPARQL specification at
>> https://www.w3.org/TR/sparql11-query/ does not require this result?   My
>> understanding is that it does.
> 
> we have been in disagreement on the conclusion, that the recommendation requires this interpretation, since the point when that example was put forward.
> 
>>
>>
>> My understanding is that, assuming that joins of empty BGPs are removed
>> everywhere, the SPARQL specification translates the above query into
>>
>> Project( ToList(Filter( exists ( BGP(?x :q :b) ) , BGP(?x :p :d) ) ) ,
>>   { ?x } )
>>
>> This expression is evaluated on the graph by first evaluating BGP(?x :p :d),
>> resulting in the singleton multiset of solutions {{ {(?x,_:c)} }}.  Then the
>> exists substitution is performed for the solution {(?x,_:c)}, resulting in
>> BGP(_:c :q :b), whose subsequent evalution results in the multiset of
>> solutions {{ {} }}, i.e., a multiset containing the empty solution.
>>
>> Because the result is not the empty multiset, the filter does not filter out
>> the solution {(?x,_:c)}.  So the result of the Filter expression is the
>> singleton multiset of solutions {{ {(?x,_:c)} }}, and then the result of the
>> entire query is the unordered list of solutions [ {(?x,_:c)} ].
>>
>> What is wrong with this analysis?
> 
> your interpretation employs blank nodes in a manner which makes no sense.
> 
> best regards, from berlin.
> ---
> james anderson | james@dydra.com | http://dydra.com

I don't understand.  How does making sense enter into the picture at all here?

All I am doing is following through the definition of SPARQL from
https://www.w3.org/TR/sparql11-query/.  Are you saying that I am doing
something that is not sanctioned by this definition?  If so, where have I gone
wrong?

peter

Received on Sunday, 2 April 2017 18:05:39 UTC