On 2/16/2015 8:31, Antoine Isaac wrote:
> 2. In data you curate, would classes accurately pinpoint validation
> targets?
>
> Very often yes, but there will be exceptions, like SKOS' S14: "A
> resource has no more than one value of skos:prefLabel per language tag."
> http://www.w3.org/TR/skos-reference/#L1567
Just to make sure we are talking about the same things here: the current
discussion in the WG distinguishes between constraints and shapes.
Constraints are individual conditions that can be verified. Constraints
may either apply to a given start node (often the subject, ?this in
SPIN) or they may be global. Global constraints can be used to
represent, for example, that "a graph must contain exactly one instance
of foaf:Person", or "for any subject, skos:prefLabel should only have
one value per language tag". (The latter is "global" because the domain
of skos:prefLabel is rdfs:Resource, i.e. there is no natural class to
attach it to - it could also be attached to the class rdfs:Resource in
case these are interpreted globally).
A "shape" is a group of non-global constraints that talk about the same
starting node. This concept is very similar to how most mainstream
technologies and OWL use classes, i.e. as a container of property
characteristics that represent similar instances. Compare it to a class
containing owl:Restrictions.
>
>>
>> 3. Anything you want to say about treating shapes themselves as
>> classes to be used in instance data?
>
>
> Using classes to represent shapes would at least require a new
> mechanism to relate these classes to the graphs where they 'apply'
> (i.e. the graphs where the specified constraint should hold). I'm not
> sure it's really great from the general perspective of RDFS/OWL as
> knowledge representation languages. I.e. we would restrict the scope
> of some classes to certain graphs, while RDFS/OWL classes have been
> defined with an open world assumption since the beginning.
The same seems to apply to "shapes" being not classes. Note that the WG
is aiming at producing a new language, i.e. none of the existing
RDFS/OWL classes would contain (LDOM) definitions yet. From the day that
the new standard would be introduced, the owners of the RDFS/OWL
ontologies can decide whether they want to define stricter constraints
on their instances or not. (Unless the WG decides to repurpose OWL for
closed-world checking, but this seems unlikely at this stage for these
very reasons). But the existing class definitions may serve as a natural
structure to attach constraints to.
Thanks,
Holger
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