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Re: ISSUE-135: Proposed changes to implement syntax simplification

From: Peter F. Patel-Schneider <pfpschneider@gmail.com>
Date: Tue, 10 May 2016 13:27:36 -0700
To: Holger Knublauch <holger@topquadrant.com>, "public-data-shapes-wg@w3.org" <public-data-shapes-wg@w3.org>
Message-ID: <4eb2e0e8-4d55-db25-5089-408829b5674c@gmail.com>

Why not also allow any component that is currently allowed in node constraints
to occur in shapes?

This permits

ex:MyShape a sh:Shape ;
        sh:or (
            [ a sh:NodeConstraint ;
                    sh:datatype xsd:string ;
                ] ;
            ]
            [ a sh:NodeConstraint ;
                    sh:class schema:Address ;
                ]
        ) .

instead of the current

ex:MyShape a sh:Shape ;
    sh:constraint [
        sh:or (
            [ a sh:Shape ;
                sh:constraint [
                    a sh:NodeConstraint ;
                    sh:datatype xsd:string ;
                ] ;
            ]
            [ a sh:Shape ;
                sh:constraint [
                    a sh:NodeConstraint ;
                    sh:class schema:Address ;
                ]
            ]
        )
    ] .

peter


On 05/08/2016 11:16 PM, Holger Knublauch wrote:
> I have meanwhile had a bit more time for this topic and here is my updated
> proposal (which is also much simpler than before).
> 
> Several WG members supported the idea of allowing constraints to be used as
> values in places such as sh:or. I was asked to make some specific suggestions
> on what would need to be changed in the spec, so that the following syntax
> options would behave identically. (Both scenarios state that the values of
> schema:address must be string literals or instances of schema:Address):
> 
> a) Currently supported: sh:or can only be used with sh:NodeConstraints and
> operands of sh:or must be shapes
> 
> ex:MyShape
>     a sh:Shape ;
>     sh:constraint [
>         sh:or (
>             [ a sh:Shape ;
>                 sh:property [
>                     sh:predicate schema:address ;
>                     sh:datatype xsd:string ;
>                 ] ;
>             ]
>             [ a sh:Shape ;
>                 sh:property [
>                     sh:predicate schema:address ;
>                     sh:class schema:Address ;
>                 ] ;
>             ]
>         )
>     ]
> 
> which lacks on multiple fronts - it is too verbose and also forces repetition
> of the predicate.
> 
> b) Proposed: generalize sh:or and values of sh:or may be sh:NodeConstraints:
> 
> ex:MyShape
>     a sh:Shape ;
>     sh:property [
>         sh:predicate schema:address ;
>         sh:or (
>             [ sh:datatype xsd:string ]
>             [ sh:class schema:Address ]
>         )
>     ]
> 
> In this proposal, the members of the sh:or List may be sh:NodeConstraints or
> sh:Shapes.
> 
> Required changes (all incremental to current spec):
> 
> 1) Rename sh:hasShape from sh:hasShape(?node, ?shape, ?shapesGraph) to
> 
>     sh:validateNode(?node, ?shapeOrConstraint, ?shapesGraph)
> 
> The algorithm would be changed to
> 
> a) if ?shapeOrConstraint rdf:type sh:Shape, then behave as currently
> b) otherwise, assume rdf:type sh:NodeConstraint
> c) report failure if the node has rdf:type that is neither sh:Shape nor
> sh:NodeConstraint.
> 
> The name sh:validateNode is better than sh:hasShape because it may also return
> unbound. I have no strong opinion whether we should assume sh:Shape or
> sh:NodeConstraint as default here - it really depends on what case we consider
> more frequent and what kind of syntactic sugar we want to provide.
> 
> 2) Generalize sh:or to also have contexts: sh:PropertyConstraint and
> sh:InversePropertyConstraint. The validators are almost identical to the
> current one, simply calling sh:validateNode on each value.
> 
> The same approach would work for sh:and and sh:not. I guess also for
> sh:valueShape if that's desirable.
> 
> Regards,
> Holger
> 
> 
> On 5/05/2016 22:21, Holger Knublauch wrote:
>> Too quick: I believe there is a glitch in the algorithm below and I need to
>> think more about the implementation details. As stated it would walk the
>> properties of a property value, which is incorrect. Maybe the list values
>> need to be interpreted as sh:NodeConstraints only. Please ignore for now.
>>
>> Holger
>>
>>
>> On 5/05/2016 12:49, Holger Knublauch wrote:
>>> Several WG members supported the idea of allowing constraints to be used as
>>> values in places such as sh:or. I was asked to make some specific
>>> suggestions on what would need to be changed in the spec, so that the
>>> following syntax options would behave identically. (Both scenarios state
>>> that the values of schema:address must be string literals or instances of
>>> schema:Address):
>>>
>>> a) Currently supported: sh:or can only be used with sh:NodeConstraints and
>>> operands of sh:or must be shapes
>>>
>>> ex:MyShape
>>>     a sh:Shape ;
>>>     sh:constraint [
>>>         sh:or (
>>>             [ a sh:Shape ;
>>>                 sh:property [
>>>                     sh:predicate schema:address ;
>>>                     sh:datatype xsd:string ;
>>>                 ] ;
>>>             ]
>>>             [ a sh:Shape ;
>>>                 sh:property [
>>>                     sh:predicate schema:address ;
>>>                     sh:class schema:Address ;
>>>                 ] ;
>>>             ]
>>>         )
>>>     ]
>>>
>>> which lacks on multiple fronts - it is too verbose and also forces
>>> repetition of the predicate.
>>>
>>> b) Proposed: generalize sh:or and values of sh:or may be constraints of the
>>> same kind as the surrounding constraint.
>>>
>>> ex:MyShape
>>>     a sh:Shape ;
>>>     sh:property [
>>>         sh:predicate schema:address ;
>>>         sh:or (
>>>             [ sh:datatype xsd:string ]
>>>             [ sh:class schema:Address ]
>>>         )
>>>     ]
>>>
>>> In this proposal, the members of the sh:or List may be
>>> sh:PropertyConstraints if sh:or is used within a sh:PropertyConstraint.
>>>
>>> Required changes (all incremental to current spec):
>>>
>>> 1) Generalize sh:hasShape from sh:hasShape(?node, ?shape, ?shapesGraph) to
>>>
>>>     sh:validateNode(?node, ?shapeOrConstraint, ?shapesGraph,
>>> ?defaultConstraintType, ?defaultPredicate)
>>>
>>> The two arguments at the end are optional, and are used to complement the
>>> provided ?shapeOrConstraint unless it is a sh:Shape. Legal values for
>>> ?defaultConstraintType would be sh:PropertyConstraint,
>>> sh:InversePropertyConstraint and sh:NodeConstraint. ?defaultPredicate is
>>> only supported if ?defaultConstraintType is given and != sh:NodeConstraint.
>>>
>>> The algorithm would be
>>>
>>> a) if ?shapeOrConstraint rdf:type sh:Shape, then behave as currently
>>> b) otherwise, assume ?defaultConstraintType (unless the node has an rdf:type)
>>>     and assume ?defaultPredicate for sh:predicate.
>>> c) report failure if the node has rdf:type that is neither sh:Shape nor
>>> ?defaultConstraintType.
>>>
>>> While this function isn't pretty it's mostly used internally anyway and may
>>> therefore be regarded as an implementation detail. The name sh:validateNode
>>> is better than sh:hasShape because it may also return unbound.
>>>
>>> 2) Generalize sh:or to also have contexts: sh:PropertyConstraint and
>>> sh:InversePropertyConstraint
>>>
>>> 3) Add a sh:propertyValidator to sh:OrConstraint similar to what we have as
>>> sh:nodeValidator, but with the sh:validateNode function:
>>>
>>> SELECT $this ?failure ...
>>> WHERE {
>>>  	{
>>> 		$this $predicate ?value .
>>> 	}
>>> 	 {
>>> 		SELECT (SUM(?s) AS ?count)
>>> 		WHERE {
>>> 			GRAPH $shapesGraph {
>>> 				$or rdf:rest*/rdf:first ?shape .
>>> 			}
>>> 			BIND (sh:validateNode(?value, ?shape, $shapesGraph, sh:PropertyConstraint, $predicate) AS ?valid) .
>>> 			BIND (IF(bound(?valid), IF(?valid, 1, 0), 'error') AS ?s) .
>>> 		}
>>> 	}
>>> 	BIND (!bound(?count) AS ?failure) .
>>> 	FILTER IF(?failure, true, ?count = 0) .
>>> }
>>>
>>> and similar for sh:inversePropertyValidator. The same approach would work
>>> for sh:and and sh:not. I guess also for sh:valueShape if that's desirable.
>>>
>>> Regards,
>>> Holger
>>>
>>
> 
Received on Tuesday, 10 May 2016 20:34:34 UTC

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