ISSUE-78: Proposal for Abstract Classes Constraint

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 SHOULD not 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. 

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 SHOULD not be instantiated directly. Every instance of an 
abstract class SHOULD also 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