- From: Holger Knublauch <holger@topquadrant.com>
- Date: Wed, 8 Jun 2016 15:09:10 +1000
- To: public-data-shapes-wg@w3.org
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
Received on Wednesday, 8 June 2016 05:09:46 UTC