Re: ISSUE-95: Proposal for model simplifications

* Peter F. Patel-Schneider <pfpschneider@gmail.com> [2015-11-19 11:05-0800]
> The cleanup of SHACL constraints could be something like:
> 
> - A constraint is either a node constraint or a global constraint.
> 
> - A node constraint is something that is true or false of nodes in a graph.
>   Node constraints can be just about anything, including SPARQL-based
>   constraints.  Node constraints include boolean constructs and closed
>   versions of constraints.
> 
> - Node constraints include property-path constraints.  A property-path
>   constraint contains a property path, perhaps some cardinality
>   constraints, and perhaps some node constraints.
>   - For example "at least 5 children and all male" or "all inverse of
>     children are people" are property-path constraints.
>   - Cardinality constraints are "at least n" or "at most n" or qualified
>     versions of these, e.g., "at least 5 are male", which contain a
>     cardinality and a node constraint.
>     a qualified cardinality constraint here ("at least 1 x is y").
>   - A property-path constraint is evaluated on a node by finding the set of
>     values of the property path from the node, checking to see if this set
>     satisfies the cardinality constraints and then checking to see if the
>     values each satisfy each of the node constraints.
>   - A set of values satisfies an unqualified cardinality constraint
>     depending only on the size of the set.  A set of values satisfies a
>     qualified cardinality constraint if the subset of the values that
>     satisfy the node constraint satisfy the cardinality.
> 
> - A global constraint is something that is true or false of a graph as a
>   whole.  All (current) global constraints are SPARQL-based.
> 
> A SHACL shape is then just a node constraint.  Shapes tend to be named, and
> used as targets of scoping (control) triples.
> 
> 
> The difference between this goes beyond Arthur's to cover qualified
> cardinalities, which don't fit into Arthur's setup; closure; and global
> constraints.
> 
> 
> The difference between node constraints and ShEx is that ShEx distinguishes
> between node constraints (Shape Expressions) and shapes (combination of
> Label and Shape Definition).

Agreed. The shape also has a <closed> flag and a list of <extra>
predicates which don't show up in constraints (see "shapeExpr" in
<http://shex.io/primer/ShExJ#h-schemaimg>).


> peter
> 

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-ericP

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Received on Tuesday, 24 November 2015 11:05:12 UTC