unexpected result of group by

[Marcel Karnstedt-Hulpus]

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Hi,

when we run queries like

SELECT ?s (count(DISTINCT ?f) AS ?cnt)
WHERE { ?s a nat:ABC . ?f ?p ?o }
GROUP BY ?s

where nat:ABC does not exist (i.e., there is no single binding for
?s), we would expect an empty result.

But we rather get the result

s cnt
0

i.e., no binding for ?s but a 0 for ?cnt.

Why is that? It unfortunately breaks our automated processing of the
query.


Thanks,
Marcel


- --
Dr. Marcel Karnstedt-Hulpus
www.marcel.karnstedt.com

Senior Data Architect
IT & Production Corporate Markets / Databases
Springer Nature
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[Zachary Whitley]

I believe that this is correct. The query will return an empty graph over which the aggregate will be applied. I think this previous discussion might be relevant to your question [1].

[1] https://groups.google.com/a/clarkparsia.com/forum/#!topic/stardog/VcO5kylcEgU

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[Zachary Whitley]

I should probably acknowledge that I only said that I think the result that you're getting is correct without providing a solution to your problem. Is there a particular reason why you can't process that response?

On Fri, Jan 20, 2017 at 9:51 AM, Zachary Whitley <zachary...@wavestrike.com> wrote:

I believe that this is correct. The query will return an empty graph over which the aggregate will be applied. I think this previous discussion might be relevant to your question [1].

[1] https://groups.google.com/a/clarkparsia.com/forum/#!topic/stardog/VcO5kylcEgU

[Evren Sirin]

Adding "HAVING (bound(?s))" at the end of the query would get rid of
the empty result.

Best,
Evren

On Fri, Jan 20, 2017 at 4:03 PM, Zachary Whitley

>>> stardog+u...@clarkparsia.com

>>> For more options, visit this group at
>>> http://groups.google.com/a/clarkparsia.com/group/stardog?hl=en
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>>>
>>
>
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[Marcel Karnstedt-Hulpus]

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Hash: SHA512

Hi Evren, Zachary,

thanks a lot for the explanation and the suggestion. Evren's hint
should indeed help us to overcome this issue.

Zachary, quick explanation: We automatically process the result of
different SPARQL queries to make sure that our data follows some sort
of contract. In this case here, the test passes when the query result
is empty. But it wasn't - although the data itself was not faulty.


Cheers,
Marcel

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[Zachary Whitley]

On Mon, Jan 23, 2017 at 8:16 AM, Marcel Karnstedt-Hulpus <marcel.k...@springernature.com> wrote:

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Hi Evren, Zachary,

thanks a lot for the explanation and the suggestion. Evren's hint
should indeed help us to overcome this issue.

Zachary, quick explanation: We automatically process the result of
different SPARQL queries to make sure that our data follows some sort
of contract. In this case here, the test passes when the query result
is empty. But it wasn't - although the data itself was not faulty.

Thanks for sharing. Sounds somewhat like what ICV does [1]. Ever try looking into using ICV for what you're doing? It might have some advantages to the approach you're using. I'm just interested in hearing how people are using Stardog, what worked, what didn't, why. etc.

[1] http://docs.stardog.com/#_validating_constraints

 

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[Marcel Karnstedt-Hulpus]

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Hi Zachary,

ICV is indeed something interesting that we briefly expected before.
We didn't use it in the first place since pure SPARQL leaves us in the
smallest technical debt for this task.

Anyhow, we'll have a look at what advantages ICV has to offer.


Cheers,
Marcel

On 23/01/2017 15:10, Zachary Whitley wrote:
>
>
> On Mon, Jan 23, 2017 at 8:16 AM, Marcel Karnstedt-Hulpus
> <marcel.k...@springernature.com

> <mailto:marcel.k...@springernature.com>> wrote:
>
> Hi Evren, Zachary,
>
> thanks a lot for the explanation and the suggestion. Evren's hint
> should indeed help us to overcome this issue.
>
> Zachary, quick explanation: We automatically process the result of
> different SPARQL queries to make sure that our data follows some
> sort of contract. In this case here, the test passes when the query
> result is empty. But it wasn't - although the data itself was not
> faulty.
>
>
>> Thanks for sharing. Sounds somewhat like what ICV does [1]. Ever
>> try looking into using ICV for what you're doing? It might have
>> some advantages to the approach you're using. I'm just interested
>> in hearing how people are using Stardog, what worked, what
>> didn't, why. etc.
>
>> [1] http://docs.stardog.com/#_validating_constraints
>
>
>
> Cheers, Marcel
>
>
> On 21/01/2017 23:28, Evren Sirin wrote:
>> Adding "HAVING (bound(?s))" at the end of the query would get
>> rid of the empty result.
>
>> Best, Evren
>
>> On Fri, Jan 20, 2017 at 4:03 PM, Zachary Whitley

>> <zachary...@wavestrike.com

> <mailto:zachary...@wavestrike.com>> wrote:
>>> I should probably acknowledge that I only said that I think
>>> the result that you're getting is correct without providing a
>>> solution to your problem. Is there a particular reason why you
>>> can't process that response?
>>>
>>> On Fri, Jan 20, 2017 at 9:51 AM, Zachary Whitley

>>> <zachary...@wavestrike.com

> <mailto:zachary...@wavestrike.com>> wrote:
>>>>
>>>> I believe that this is correct. The query will return an
>>>> empty graph over which the aggregate will be applied. I think
>>>> this previous discussion might be relevant to your question
>>>> [1].
>>>>
>>>> [1]
>>>> https://groups.google.com/a/clarkparsia.com/forum/#!topic/stardog/VcO5kylcEgU
>
>>>>

<https://groups.google.com/a/clarkparsia.com/forum/#%21topic/stardog/VcO5kylcEgU>

>>>>
>>>>
>>>>
> On Fri, Jan 20, 2017 at 5:36 AM, Marcel Karnstedt-Hulpus

>>>> <marcel.k...@springernature.com

> <mailto:marcel.k...@springernature.com>> wrote:
>>>>>
>> Hi,
>
>> when we run queries like
>
>> SELECT ?s (count(DISTINCT ?f) AS ?cnt) WHERE { ?s a nat:ABC . ?f
>> ?p ?o } GROUP BY ?s
>
>> where nat:ABC does not exist (i.e., there is no single binding
>> for ?s), we would expect an empty result.
>
>> But we rather get the result
>
>> s cnt 0
>
>> i.e., no binding for ?s but a 0 for ?cnt.
>
>> Why is that? It unfortunately breaks our automated processing of
>> the query.
>
>
>> Thanks, Marcel
>
>
>>>>>
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>>>>> <mailto:sta...@clarkparsia.com> To
> unsubscribe from this group,
>>>>> send email to stardog+u...@clarkparsia.com
> <mailto:stardog%2Bunsu...@clarkparsia.com> For more

>>>>> options, visit this group at
>>>>> http://groups.google.com/a/clarkparsia.com/group/stardog?hl=en
>
>>>>>

<http://groups.google.com/a/clarkparsia.com/group/stardog?hl=en>
>>>>>
>>>>>
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>>>>>
>>>>
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