Re: shapes-ISSUE-168 (instance count): How to constrain number of instances of a class in a graph [SHACL - Core]

On 18/06/2016 4:47, Karen Coyle wrote:
> Interesting. Can you point out where this is explained in the spec? - kc

In the beginning of section 4, when you scroll down to the definition of 
value nodes:

  * Fornode constraints
    <http://w3c.github.io/data-shapes/shacl/#dfn-node-constraints>thevalue
    nodesare the individualfocus nodes
    <http://w3c.github.io/data-shapes/shacl/#dfn-focus-node>, forming a
    set of exactly one node.

The spec doesn't have to be written that way, and there are arguments in 
favor of changing it so that it applies to
- either all scope nodes (when called from the top-level)
- or just the focus node (when called as nested shape, e.g. via 
sh:shape, sh:or)

Maybe we can resolve this next week too.

Holger


>
> On 6/17/16 10:22 AM, Irene Polikoff wrote:
>> The way I understand it, when one uses scopeClass, the constraints apply
>> to each SHACL instance of a class individually. For example, each 
>> instance
>> of a Person can have only two parents. And a condition is tested against
>> each node individually.
>>
>> This constraint, however, doesn¹t apply to each instance 
>> individually. It
>> is about the number of all instances. This is quite different, so I
>> wouldn¹t expect to use scopeClass.
>>
>> Irene
>>
>>
>>
>>
>>
>>
>> On 6/17/16, 1:10 PM, "Karen Coyle" <kcoyle@kcoyle.net> wrote:
>>
>>> My preference overall would be to not use classes at all in validation;
>>> to have all operations on triples, and rdf:type would be simply a
>>> predicate like any other. (I believe that ShEx takes this approach.)
>>> However, if you encourage people to view the objects of rdf:type as
>>> classes, then you have to allow them to do so throughout, otherwise it
>>> becomes difficult to explain "when is a class not a class?".
>>>
>>> With the solution in this proposal, we have what to the user is a class
>>> but it does not use scopeClass, and scopeNode binds to the subject of a
>>> triple, AFAI can determine. The below would not match the schema.org
>>> example.[1]
>>>
>>> kc
>>> [1] http://schema.org/FlightReservation
>>>
>>>
>>> On 6/13/16 5:04 AM, RDF Data Shapes Working Group Issue Tracker wrote:
>>>> shapes-ISSUE-168 (instance count): How to constrain number of 
>>>> instances
>>>> of a class in a graph [SHACL - Core]
>>>>
>>>> http://www.w3.org/2014/data-shapes/track/issues/168
>>>>
>>>> Raised by: Holger Knublauch
>>>> On product: SHACL - Core
>>>>
>>>> There was recent discussion about how to specify min/max numbers of
>>>> instances in a graph.  Off-list I had also received a question from
>>>> schema.org people about how to state that a graph/message must have
>>>> exactly one instance of schema:FlightReservation, possibly to ensure
>>>> that a graph has a starting point/root for validation.
>>>>
>>>> A possible syntax that would easily work with the current architecture
>>>> could be
>>>>
>>>> ex:MyShape
>>>>     a sh:Shape ;
>>>>     sh:scopeNode schema:FlightReservation ;
>>>>     sh:constraint [
>>>>         sh:minInstanceCount 1 ;
>>>>         sh:maxInstanceCount 1 ;
>>>>     ] .
>>>>
>>>>
>>>>
>>>>
>>>
>>> -- 
>>> Karen Coyle
>>> kcoyle@kcoyle.net http://kcoyle.net
>>> m: 1-510-435-8234
>>> skype: kcoylenet/+1-510-984-3600
>>>
>>
>>
>>
>