Re: ISSUE-78: Proposal for Abstract Classes Constraint

On Apr 11, 2016 2:03 PM, "Jim Amsden" <jamsden@us.ibm.com> wrote:
>
> re: ISSUE-78: Abstract Classes: There is no use case or requirement for
SHACL to support abstract classes, but the issue provides reasonable
motivation and the votes on the issue are >0.
>
> The current spec contains the following paragraph in section  2.1.2.1
Implicit Class Scopes:
>
> Classes may be declared to be abstract by setting their property
sh:abstract to true. Abstract classes SHOULDnot be instantiated directly,
i.e. every instance of an abstract class SHOULD also have an rdf:type
triple to a non-abstract subclass of the abstract class.

Most of SHACL doesn't depend on your triple's. Perhaps it would be more
practical to say that validating a focus node as abstract class succeeds if
the node matches exactly one leaf shape. A leaf shape is any shape C which
is derived from another shape A where there is no shape derived from C.

+1 to Karen's MUST comments.

> where "Classes" references sh:ShapeClass. The concept of abstract class
could instead be expressed as a node constraint. This would allow a class
to be abstract or concrete in different situations based on the domain
needs.
>
> Proposal:
>
> Remove the paragraph about abstract classes from section 2.1.2.1.
>
> Add sh:abstract to the table in section 3 and indicate that it is a
sh:NodeConstraint.
>
> Add section 3.10 Abstract Class Constraint
>
> Classes may be constrained to be abstract by creating a node constraint
with class scope, and including the sh:isAbstract  property set to true.
Abstract classes SHOULDnot be instantiated directly. Every instance of an
abstract class SHOULDalso have an rdf:type triple to a non-abstract
subclass of the abstract class.
>
> #Example abstract class constraint:
>
> ex:AnAbstractClassConstraint
>      a sh:Shape ;
>      sh:scopeNode ex:AnAbstractClass ;
>      sh:isAbstract true .
>
> #Example graph data
>
> ex:AnAbstractClass
>      a rdfs:Class ;
>      dcterms:title "Example of an abstract class constraint." .
>
> Jim Amsden, Senior Technical Staff Member
> OSLC and Linked Lifecycle Data
> 919-525-6575
>