Re: Improving EXISTS

On 07/01/2016 10:20 PM, james anderson wrote:
> 
>> On 2016-07-01, at 22:47, Peter F. Patel-Schneider <pfpschneider@gmail.com
>> <mailto:pfpschneider@gmail.com>> wrote:
>>
>> On 07/01/2016 01:34 PM, james anderson wrote:
>>> good evening;
>>>
>>>> On 2016-06-30, at 15:05, Peter F. Patel-Schneider <pfpschneider@gmail.com
>>>> <mailto:pfpschneider@gmail.com>
>>>> <mailto:pfpschneider@gmail.com>> wrote:
>>>>
>>>> On 06/30/2016 04:50 AM, Axel Polleres wrote:
>>>>> Dear Andy,
>>>>>
>>>>> [...]
>>>>>
>>>>> I have to admit I couldn't follow the whole discussion but is there a
>>>>> mail/link which summarizes the issues (I am aware of the bnode injection
>>>>> issue, which more there are?)
>>>>>
>>>>> Thanks & best regards,
>>>>> Axel
>>>>
>>>> Hi Axel:
>>>>
>>>> I don't think that there is an email that is exactly what you asked for so I
>>>> have tried to put together a simple list of problems with EXISTS.  The first
>>>> two problems are directly problems with the spec.  The last three are cases
>>>> where the spec produces what can be considered to be counterintuitive results
>>>> and some implementations diverge from the spec.
>>>>
>>>> […]
>>>
>>> note that, in the issue descriptions which followed, the conclusions are
>>> subject to discussion, as they follow from interpretations of the
>>> recommendation which are not universal.
>>>
>>> best regards, from berlin,
>>
>> Which conclusions and interpretations of the recommendation are not universal
>> in this message?
> 
> the ones which follow from an interpretation of the recommendation’s authors
> intent, which stipulates mechanisms which are oblivious to thirty year old
> insights into variable capture and identifies parser and run-time data models.
> 
> in light of the demonstrated deficiencies of the results implied of that
> interpretation, it may be more fruitful to explore alternatives which yield
> results more in keeping with the recommendation’s intent.
> a summary of the disagreement appears at the top of an early post in the thread: 
> 
>     https://lists.w3.org/Archives/Public/public-sparql-dev/2016AprJun/0047.html
> 
> best regards from berlin,
> ---
> james anderson | james@dydra.com <mailto:james@dydra.com> | http://dydra.com

I believe that the specification of EXISTS in
https://www.w3.org/TR/2013/REC-sparql11-query-20130321/ is badly broken.  I
believe that the specification there has multiple problems and needs to be
changed.  I pointed out what I believe are five different problems with the
spec, as written.

I believe that the spec needs to be changed.  I believe that it is not just a
matter of filling in some holes in an obvious way, but that the spec clearly
says that certain SPARQL queries with EXISTS are to be interpreted in a way
that violates definitions in the spec or that produce results that are counter
to intuitions.

If an appeal to the intentions of the SPARQL Working Group or to notions of
variable capture can produce solutions to all these problems then great.
I don't think that this means that there is no need to do anything, however.
There is at least one of these cases where different SPARQL implementations
produce different results.  Even where all current SPARQL implementations
differ from the spec in the same way it is useful to have something that
documents and supports this difference from the spec.

I believe that a successful attempt to produce errata to the spec that has
general backing is going to have to start with a description of what the spec
says that is problematic.  That is what I tried to do in my message to Axel.
Are you saying that some of these cases are not problematic?  Are you saying
that I said something counter to what the spec says?  If so, please say which
parts of my message you think are incorrect.

peter

Received on Saturday, 2 July 2016 10:40:52 UTC