Re: using classes to control constraints

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In RDF (not RDFS) class membership can only be directly asserted, by means
of rdf:type triples.  In RDFS you can assert class membership and via
subclassing infer membership in other superclasses.  However, this all
directly depends on asserting class membership via rdf:type triples.

You never (at least as far as I can tell) assert membership in a shape.
Instead a shape provides recognition conditions that precisely determine
which nodes in a graph belong to the shape.  A shape implementation turns
this determination into a procedural process.  You can then ask whether a
node in a graph belongs to a shape.

So, although shapes and RDF(S) classes are indeed related to sets, and one
can talk about the members of a shape and the members of an RDF(S) class,
there are distinct differences between the two.


In some modelling languages there are constructs that are both classes and
shapes.  For example, OWL descriptions work this way.  You can assert that
an object belongs to a description and you can also recognize whether an
object belongs to a description.  For many descriptions, this recognition
process does not depend at all on any explicit typing assertions.


What would it mean to assert that an object belongs to a ShExC shape via an
rdf:type link?


peter


On 02/11/2015 08:09 AM, Irene Polikoff wrote:
> Peter,
> 
> Could you clarify this more? I don't see the contrast you are trying to 
> communicate and I am not sure what you mean by "recognized".
> 
> Class membership is asserted. However, it can also be inferred which I
> am interpreting the same as "recognized".
> 
> I don't think membership in the shape is recognized if by "recognized"
> you mean that there is some computational process that decides whether
> something is a member of a shape or not. It is asserted in a sense that a
> statement is made about the membership.
> 
> In the end, however, they both have members.
> 
> Irene
> 
> On Wed, Feb 11, 2015 at 9:33 AM, Peter F. Patel-Schneider 
> <pfpschneider@gmail.com <mailto:pfpschneider@gmail.com>> wrote:
> 
> Classes are things that you assert membership in.  Shapes are things
> that you recognize membership in.
> 
> I'm certainly open to other syntaxes.
> 
> peter
> 
> 
> 
> On 02/09/2015 09:19 PM, Holger Knublauch wrote:
>> Hi Peter,
> 
>> your email below seems to clarify how OWL Closed World would work. But
>> I don't see a response to my questions at the end of my previous email
>> in this thread (at the bottom here), especially on whether you would
>> accept any other syntax than OWL at all.
> 
>> Thanks, Holger
> 
> 
> 
> 
>> On 2/8/2015 8:26, Peter F. Patel-Schneider wrote: In OWL constraints
>> for RDF, OWL axioms are used as constraints.  However, this doesn't
>> make RDF(S) classes be constraints.
> 
>> You still create RDFS ontologies in the normal way, and constraints 
>> don't have a role to play there.  Or maybe you don't have an ontology
>> at all.
> 
>> It is only when you want to validate some data that the constraints
>> play a role at all, and the constraints don't play the role of classes
>> or even part of the description of a class.  You can have multiple
>> constraint sets that employ classes from a particular ontology
>> depending on just how your data needs to be.
> 
>> Note in particular that if you need named shapes (a.k.a. closed world 
>> recognition) that these named shapes are only used for recognition, 
>> i.e., there are no type links that make individuals belong to these 
>> shapes.
> 
> 
>> peter
> 
> 
> 
> 
>> On 02/07/2015 01:35 PM, Holger Knublauch wrote:
>>>>> On 2/8/15 12:44 AM, Peter F. Patel-Schneider wrote:
>>>>>> I am very strongly in favour of having shapes be different
>>>>>> from RDFS classes
>>>>> Hi Peter, would you mind explaining your statement above? Your 
>>>>> original proposal to the WG was OWL Closed World, which 
>>>>> re-interprets restrictions with closed world meaning:
>>>>> 
>>>>> ex:Class a owl:Class ; rdfs:subClassOf [ a owl:Restriction ; 
>>>>> owl:onProperty ex:property ; owl:minCardinality 1 ; ] .
>>>>> 
>>>>> The equivalent in LDOM is:
>>>>> 
>>>>> ex:Class a owl:Class ; ldom:property [ a ldom:PropertyConstraint
>>>>> ; ldom:predicate ex:property ; ldom:minCount 1 ; ] .
>>>>> 
>>>>> Where do these approaches differ? If you would not accept the 
>>>>> second syntax, do you have any other syntax than OWL that you
>>>>> would accept?
>>>>> 
>>>>> Thanks Holger
>>>>> 
>>>>> 
> 
> 
> 
> 
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Received on Wednesday, 11 February 2015 16:40:43 UTC