Re: ISSUE-139: uniform descriptions and implementations of constraint components

Holger, that still doesn't explain what the difference is. What is the 
quality of a SHACL class that is different to a triple with a predicate 
of rdf:type? Are you saying that scopeClass implies/allows subclass 
relationships to be included? If so, that must be said in the 
specification, and it should be illustrated in the examples. As it is, 
the examples given would have the same result using either predicate.

Also, the section that introduces scopeNode does not say that it applies 
only to the subject of a triple. If that is the case, then it needs to 
specify that.

kc

On 6/8/16 9:44 PM, Holger Knublauch wrote:
>
> On 9/06/2016 14:40, Karen Coyle wrote:
>> sh:scopeClass <foaf:Person> and sh:scopeNode <foaf:Person> appear to
>> identify the same focus node(s) in the data graph.
>
> sh:scopeNode means "the (class) node itself".
> sh:scopeClass means "all SHACL instances of the class".
>
> So they do not identify the same focus nodes.
>
> Holger
>
>
>
>>
>> ***shape1***
>> ex:MyShape
>>     a sh:Shape ;
>>     sh:scopeNode foaf:Person ;
>>     sh:inverseProperty [
>>         sh:predicate rdf:type ;
>>         sh:maxCount 2 ;
>>     ] .
>>
>> ***shape2***
>> ex:PersonShape
>>     a sh:Shape ;
>>     sh:scopeClass ex:Person .
>>
>> ***data graph***
>>
>> ex:Alice a ex:Person .
>> ex:Bob a ex:Person .
>> ex:NewYork a ex:Place .
>>
>> Where does the spec address the reason for this?
>>
>> kc
>>
>> On 6/7/16 10:09 PM, Holger Knublauch wrote:
>>>
>>>
>>> On 8/06/2016 14:57, Karen Coyle wrote:
>>>>
>>>>
>>>> On 6/7/16 7:38 PM, Holger Knublauch wrote:
>>>>> Yes and SHACL should implement the same policy, because sh:maxCount
>>>>> also
>>>>> only makes sense for predicate-based constraints and not node
>>>>> constraints.
>>>>
>>>> Does this then rule out a constraint like "n things of type x"? For
>>>> example, if you want to limit the number of foaf:Person nodes?
>>>
>>> No. To express "A graph must have at most 2 instances of foaf:Person"
>>> you would write
>>>
>>> ex:MyShape
>>>     a sh:Shape ;
>>>     sh:scopeNode foaf:Person ;
>>>     sh:inverseProperty [
>>>         sh:predicate rdf:type ;
>>>         sh:maxCount 2 ;
>>>     ] .
>>>
>>> In other words "there must be at most 2 triples that have foaf:Person as
>>> object and rdf:type as predicate".
>>>
>>> Peter's suggested use of sh:maxCount at node constraints would mean
>>>
>>> "Verify that the set of value nodes is not larger than two. Oh, and
>>> regardless of the actual data, I already know that this set of value
>>> nodes has size 1, because it always consists of the focus node only. So
>>> actually I only need to test whether the value of sh:maxCount > 0."
>>>
>>> which is a rather useless construct. You have just confirmed that
>>> misusing sh:maxCount as node constraints will likely confuse users.
>>>
>>> Is this difference clearer now, or what else could I clarify?
>>>
>>> Thanks,
>>> Holger
>>>
>>>
>>>
>>
>
>
>

-- 
Karen Coyle
kcoyle@kcoyle.net http://kcoyle.net
m: 1-510-435-8234
skype: kcoylenet/+1-510-984-3600

Received on Thursday, 9 June 2016 05:34:03 UTC