- From: Eric Prud'hommeaux <eric@w3.org>
- Date: Fri, 23 Jan 2015 04:27:45 -0500
- To: Dimitris Kontokostas <kontokostas@informatik.uni-leipzig.de>
- Cc: Holger Knublauch <holger@topquadrant.com>, RDF Data Shapes Working Group <public-data-shapes-wg@w3.org>
* Dimitris Kontokostas <kontokostas@informatik.uni-leipzig.de> [2015-01-23 11:03+0200] > First of all, great work initiating this Holger!!! > > Maybe I miss something in the semantics of the class declarations but I > would suggest a simplification of the constraint definitions. Examples: > > # class example > > ex:constraintA > a ldom:ClassConstraint ; > ldom:class ex:ClassA, ex:ClassB, ex:ClassC ; # (oslc:describes) > ldom:sparql """ ..?this ... """ ; > ldom:property [ > ldom:predicate ex:propA ; > ldom:minCount 1 ; > ] ; > > in this case, all classes (A,B & C) have a min cardinality 1 restriction on > ex:propA which is not possible if we subclass the constraint to a single > class. > We also decouple the schema declaration with the constraint declaration (*) > > # global constraint example, the rdfs:Resource / owl:Thing declaration is > redundant > > ex:constraintB > a ldom:GlobalConstraint ; > ldom:sparql """ ... """ ; > > # ShExC / RS shapes in a similar way these are currently defined > ex:constraintC > a ldom:ShapeConstraint ; > ldom:sparql """ ... """ ; > ldom:property [ > ldom:predicate ex:propA ; > ldom:minCount 1 ; > ] ; > > For the ShapeConstraints we can define how validation can performed e.g. > starting from a node or inferring the types of the nodes based on the shape > definition and then validating in a similar way to the ClassConstraint. > Would something like this solve the class/shape problem? If I understand you, you propose that § 2. Class Declarations be instead Shape Declarations. I believe this addresses the issues raised in the November Class vs. Shape wars: https://lists.w3.org/Archives/Public/public-data-shapes-wg/2014Nov/thread#msg37 https://lists.w3.org/Archives/Public/public-data-shapes-wg/2014Nov/thread#msg199 I believe the answer to the Can Shapes always be Classes thread https://lists.w3.org/Archives/Public/public-data-shapes-wg/2014Nov/thread#msg22 was "no", at least not for classes used elsewhere in the enterprise or public. — > (*) Another reason for not defining constraints as classes is that > automated Agents try to profile datasets for classes / properties used > which, might confuse them and give false statistics. This seems sort of like the difference between classes and interfaces in Java. (They're the same thing in C++, which is why C++ is so much more popular than Java.) > Best, > Dimtiris > > > On Fri, Jan 23, 2015 at 5:57 AM, Holger Knublauch <holger@topquadrant.com> > wrote: > > > May I suggest we try to resolve the long-standing issue of Shapes versus > > Classes in the specific context of LDOM. Maybe we can make progress if we > > have a specific metamodel in front of us. > > > > In the current draft, class definitions are containers of constraints, i.e. > > > > rdfs:Class > > a rdfs:Class ; > > rdfs:subClassOf rdfs:Resource ; > > ldom:property [ > > ldom:predicate ldom:constraint ; > > ldom:valueType ldom:Constraint ; > > ] ; > > ldom:property [ > > ldom:predicate ldom:property ; > > ldom:valueType ldom:PropertyConstraint ; > > ] ; > > > > which means that you can define a class such as > > > > ex:Rectangle > > ldom:property [ > > ldom:predicate ex:height ; > > ... > > ] ... > > > > This could (easily) be generalized by moving the properties into a new a > > class > > > > ldom:Shape > > a rdfs:Class ; > > rdfs:subClassOf rdfs:Resource ; > > ldom:property [ > > ldom:predicate ldom:constraint ; > > ldom:valueType ldom:Constraint ; > > ] ; > > ldom:property [ > > ldom:predicate ldom:property ; > > ldom:valueType ldom:PropertyConstraint ; > > ] ; > > > > which serves as superclass of rdfs:Class > > > > rdfs:Class > > a rdfs:Class ; > > rdfs:subClassOf ldom:Shape ; > > > > This would mean that users could define stand-alone shapes > > > > ex:MyShape > > a ldom:Shape ; > > ldom:property [ > > ... > > ] ... > > > > And this shape could be reused such as in > > > > ex:MyClass > > a rdfs:Class ; > > ldom:constraint [ > > a ldom:ShapeConstraint ; > > ldom:all ex:MyShape ; > > ] ... > > > > or as an entry point to the validation: > > > > FILTER ldom:violatesConstraints(?resource, ex:MyShape) > > > > (maybe renaming the function above to ldom:hasShape). > > > > Since rdfs:Class is a subclass of ldom:Shape, class definitions become > > special kinds of shape definitions. The main differences between classes > > and shapes would be: > > > > - Classes can be instantiated, i.e. you can have ex:MyRectangle a > > ex:Rectangle > > - Class-based constraints get inherited (Shapes cannot have > > rdfs:subClassOf) > > > > I don't see practical problems with such a design, and in fact it may be a > > cleaner separation of concerns. The reason why these two concepts are > > currently merged into one is that the differences are fairly small, and > > people could simply define an anonymous (even typeless) class as a > > collection of constraints, as in Example 9 > > > > http://spinrdf.org/ldomprimer.html#template-constraints > > > > Thoughts? > > > > Cheers, > > Holger > > > > > > > > > -- > Dimitris Kontokostas > Department of Computer Science, University of Leipzig > Research Group: http://aksw.org > Homepage:http://aksw.org/DimitrisKontokostas -- -ericP office: +1.617.599.3509 mobile: +33.6.80.80.35.59 (eric@w3.org) Feel free to forward this message to any list for any purpose other than email address distribution. There are subtle nuances encoded in font variation and clever layout which can only be seen by printing this message on high-clay paper.
Received on Friday, 23 January 2015 09:27:51 UTC