Re: updated draft

good evening;

> On 2017-04-02, at 20:05, Peter F. Patel-Schneider <pfpschneider@gmail.com> wrote:
> 
> 
> 
> 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?

you misconstrue the notion of “substitution”.



---
james anderson | james@dydra.com | http://dydra.com

Received on Sunday, 2 April 2017 18:24:12 UTC