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on constraints

From: Peter F. Patel-Schneider <pfpschneider@gmail.com>
Date: Thu, 29 Sep 2016 17:46:44 -0700
To: "public-rdf-shapes@w3.org" <public-rdf-shapes@w3.org>
Message-ID: <6b46b9e1-e2f1-53de-961f-8e37ccaec29e@gmail.com>
What are constraints?  What are constraint components?  What are constraint
component parameters?  The document appears to be contradictory about what
is what.

Relevant quotes from the SHACL document:

"Constraints are defined within a shape and sh:Constraint is the SHACL
superclass of all constraint types."

What counts as "defining" a constraint?

"Focus node constraints define constraints about the focus node itself."

How can a constraint define a constraint?

"Focus node constraints are attached directly to Shapes"

Not any more.

"sh:shape can be used to group focus node constraints."

Not any more, except by using sh:shape itself, I guess.

"The class sh:Shape is defined as rdfs:subClassOf sh:Constraint."

"Some constraint components have only a single parameter. For example
sh:ClassConstraintComponent has the single parameter sh:class.  These
parameters may be used multiple times within the same constraint node."

How can anything be "within" a node?

"Parameters of constraint components that have more than one parameter, such
as sh:PatternConstaintComponent, are not allowed to be used more than once
in the same constraint."

"A recursive shape is a shape thar refers to itself directly or transitively
via shape-based constraint components (i.e. sh:shape)"

"4.8.1 sh:shape

The property sh:shape can be used verify that all value nodes must have a
given shape. The value type of sh:shape is sh:Shape, but the rdf:type triple
of those shapes can be omitted.

Constraint Component: sh:ShapeConstraintComponent
Property 	Value Type 	Summary
sh:shape 	sh:Shape 	The required shape of all value nodes"

Peter F. Patel-Schneider
Nuance Communcations
Received on Friday, 30 September 2016 00:47:17 UTC

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