Re: shapes-ISSUE-91 (hsolbrig): Default Cardinality [SHACL Spec]

* Dimitris Kontokostas <kontokostas@informatik.uni-leipzig.de> [2015-09-28 10:02+0300]
> On Mon, Sep 28, 2015 at 1:17 AM, Arthur Ryman <arthur.ryman@gmail.com>
> wrote:
> 
> > I vote -1 to defining optional values for any constraint.
> >
> > The current design is consistent in its treatment of absent
> > constraints, namely that they do not lead to any checks. It is
> > therefore inconsistent to say that if minCount or maxCount are absent
> > then they are in effect present with some default value. If is
> > especially inconsistent to assign default values that give a result
> > different than if the constraints were absent.
> >
> 
> I agree with Arthur here, all constraints should be explicitly stated in
> the SHACL graph.

The usual motivation for no-defaults is that what you learn from
inferencing can contradict what you understood with less or no
inferencing. A screw case in our example would be:

  my:minCard owl:samePropertyAs sh:minCount .
  my:FooShape sh:property [
      sh:predicate foaf: name ;
      my:minCard 2       # ooo, sneaky
    ] .

You'll note, however, that this screw case arises regardless of
whether the default min cardinality is 0 or 1. I think we should just
say "a SHACL engine is not expected to perform any inferencing" and
pick defaults that are attractive to folks working in e.g. JSON-LD.

I maintain my support for default [1..1] cardinality. Regardless, we
need a way to express an unlimited max cardinality.


> - Dimitris
> 
> 
> 
> -- 
> Dimitris Kontokostas
> Department of Computer Science, University of Leipzig & DBpedia Association
> Projects: http://dbpedia.org, http://http://aligned-project.eu,
> http://rdfunit.aksw.org
> Homepage:http://aksw.org/DimitrisKontokostas
> Research Group: http://aksw.org

-- 
-ericP

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(eric@w3.org)
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Received on Monday, 28 September 2015 08:26:15 UTC