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$this in Aggregations (was: Quick Comments on https://www.w3.org/TR/2016/WD-shacl-20160814/)

From: Holger Knublauch <holger@topquadrant.com>
Date: Fri, 23 Sep 2016 14:52:04 +1000
To: public-rdf-shapes@w3.org
Message-ID: <6e68d869-d7e6-32b4-601e-423409f5d28e@topquadrant.com>
(In order to prevent a deeply nested email thread that goes across 
multiple topics, I am splitting the remaining issues into individual 
emails).

On 23/09/2016 11:36, Peter F. Patel-Schneider wrote:
>
>> aggregation
>>
>> The prohibition "Furthermore, any query that uses the variable $this in an
> aggregation is invalid." is vague. It appears to disallow the use of $this
> in any part of the SPARQL 1.1 aggregation machinery, as the pointer in the
> sentence is to Section 11 of the SPARQL specification. This would rule out
> all of the examples of aggregation in the SHACL document.
>>      Comment (HK): I have tried to clarify that this is only about the use
> of ?this in expressions. This is allowing its use in GROUP BY, in case you
> were referring to this. Apart from that I don't see uses of ?this in
> aggregations in the SHACL document.
> https://github.com/w3c/data-shapes/commit/0c6939ba95ffd6c7fee2285a3638c144a97f8528
>
> GROUP BY is part of aggregation.  There were four examples of GROUP BY ?this
> which the mentioned wording appears to prohibit.  The current wording is no
> better.  "[T]he expression used in an aggregation" is an incorrect
> description as there can be multiple expressions in the aggregation portion
> of a query.  The argument to GROUP BY itself is just as much an expression
> as the argument to HAVING.
>
> This situation is indicative of the sloppiness of the current specification.
> SPARQL has a complicated grammar.  The argument to GROUP BY is a sequence of
> GroupCondition; the argument to HAVING is a sequence of HavingCondition.
> Using general words, like "expression", to describe bits of the SPARQL
> grammar is generally incorrect.  Where specific bits of SPARQL are used in
> the SHACL definition they need to be described as they are in the SPARQL
> definition.

I have clarified this by pointing at the specific Aggregate construct in 
the SPARQL syntax:

https://github.com/w3c/data-shapes/commit/6501260d135dde1ff05b86b71b8c3835dab9dd03

Holger
Received on Friday, 23 September 2016 04:52:37 UTC

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