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Formal objection to removing features from node shapes

From: Peter F. Patel-Schneider <pfpschneider@gmail.com>
Date: Fri, 24 Feb 2017 18:57:40 -0800
To: "public-rdf-shapes@w3.org" <public-rdf-shapes@w3.org>
Message-ID: <f99ed26f-8257-c061-198e-12015ad70c46@gmail.com>
This is a formal objection to the decision of the RDF Data Shapes working
group to reclose ISSUE-139 by making node shapes ill-formed if they use any
of sh:minCount, sh:maxCount, sh:uniqueLang, sh:equals, sh:disjoint,
sh:lessThan, sh:lessThanOrEquals, or sh:qualifiedValueShape.

Node shapes that use any of these properties have suitable obvious
definitions so there is no problem adding them back to SHACL.

With the resolution node shapes and property shapes have different features.
This difference complicates the language, making it harder to explain to
users and harder to machine-generate.  Because the language is more complex
implementations become more complex and testing becomes more complex.

Removing these node shapes from the language causes a decided drop in
expressive power.  For example,

ex:s1 rdf:type sh:NodeShape ;
 sh:targetClass ex:C1 ;
 sh:disjoint ex:p1 .

checks that SHACL instances of ex:C1 do not have themselves as a value for
ex:p1.   This useful ability cannot be obtained through any other means.

So the resolution to close ISSUE-139 removes useful expressive power from
SHACL without appreciably reducing implementation or testing costs or
reducing user confusion.  All these features need to be added back to node
shapes.

Peter F. Patel-Schneider
Nuance Communications
Received on Saturday, 25 February 2017 02:58:17 UTC

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