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Re: SHACL syntax and metamodel complexity

From: Irene Polikoff <irene@topquadrant.com>
Date: Thu, 3 Mar 2016 20:57:27 -0500
Message-Id: <F61B8A19-AFBF-4207-8FAE-99F68A30877C@topquadrant.com>
Cc: Arnaud Le Hors <lehors@us.ibm.com>, kcoyle@kcoyle.net, public-data-shapes-wg@w3.org
To: "Peter F. Patel-Schneider" <pfpschneider@gmail.com>
The only reason one would have multiple min and max counts is by mistake. To me, allowing this would be akin to encouraging errors and misunderstandings - thus, not a good idea. Prohibiting it, on the other hand, seems like a helpful thing and a good idea. 

Irene

Sent from my iPhone

> On Mar 3, 2016, at 5:45 PM, Peter F. Patel-Schneider <pfpschneider@gmail.com> wrote:
> 
>> On 03/03/2016 01:42 PM, Arnaud Le Hors wrote:
>> "Peter F. Patel-Schneider" <pfpschneider@gmail.com> wrote on 03/03/2016
>> 12:14:55 PM:
>> 
>>> From: "Peter F. Patel-Schneider" <pfpschneider@gmail.com>
>>> To: kcoyle@kcoyle.net, public-data-shapes-wg@w3.org
>>> Date: 03/03/2016 12:16 PM
>>> Subject: Re: SHACL syntax and metamodel complexity
>>> 
>>>> On 03/01/2016 09:20 PM, Karen Coyle wrote:
>>>> 
>>>> 
>>>>> On 3/1/16 10:11 AM, Peter F. Patel-Schneider wrote:
>>>>> in a simple extension of the current SHACL RDF syntax this would be
>>>>> 
>>>>>      [ a sh:propertyConstraint ;
>>>>>        sh:predicate ex:p ;
>>>>>        sh:minCount 1 ;
>>>>>        sh:class ex:c ;
>>>>>        sh:maxCount 5 ;
>>>>>        sh:class ex:d ;
>>>>>        sh:minCount 3 ]
>>>> 
>>>> Doesn't this require that there be order among the triples?
>>> Otherwise, how do
>>>> the two minCount's apply to the correct sh:Class triple?
>>>> 
>>>> kc
>>> 
>>> No.  This is not a qualified cardinality.  What this says is that
>>> there is at least one value for ex:p, that all values for ex:p belong to ex:c,
>>> that there are at most 5 values for ex:p, that all values for ex:p belong to
>>> ex:d, and that there are at least three values for ex:p.
>> 
>> Ok, but the two minCounts are confusing. The first one (sh:minCount 1) is
>> essentially overridden by the second (sh:minCount 3), right? So, why did you
>> choose to have them both? What's the significance?
>> --
>> Arnaud  Le Hors - Senior Technical Staff Member, Open Web Technologies - IBM
>> Software Group
> 
> Right now, the SHACL syntax does not allow multiple minCounts, or multiple
> sh:class, or multiple anything.  Multiple minCounts are not useful.  Multiple
> sh:class values are, however, and I view this as something that is going to be
> a pain point.
> 
> Why are multiple sh:class values not allowed?  Well, multiples are hard to
> deal with if they are like the current design of qualified cardinality, where
> there are two property values that need to be combined.  So to permit the
> useful multiples one has to find a way to get around the combinations.
> 
> The combinations are also problematic from a syntax viewpoint, as it may be
> hard to see the combination.  Thus my proposal is to refactor these syntactic
> constructs.  The result allows for repetition where useful and permits it even
> when it is not (very) useful.  Will users ever have multiple minCounts (on
> purpose)?  Probably not, but forbidding them doesn't seem like a good idea.
> 
> peter
> 
> 
Received on Friday, 4 March 2016 02:29:50 UTC

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