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Looking at the current proposals for SHACL

From: Peter F. Patel-Schneider <pfpschneider@gmail.com>
Date: Thu, 19 Mar 2015 17:03:12 -0700
Message-ID: <550B63C0.9040509@gmail.com>
To: RDF Data Shapes Working Group <public-data-shapes-wg@w3.org>
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There was some spirited discussion at the WG teleconference today, and then
some spirited IRC chat afterwards.  This all prompted me to take another
look at what proposals for SHACL that are being put forward in the WG at
this point in time.

I see four relevant documents.

1/ http://w3c.github.io/data-shapes/semantics/

This document contains an informal description of a core for SHACL

Significant Features:
- - It does not contain a formal specification.
- - It presents only a core of SHACL.
- - The core contains potentially recursive shapes, but not closed shapes or
  global constraints.
- - The description of recursive shapes appears to be ill-founded.
- - It does not discuss violation reporting.
- - It only has a few methods for controlling evaluation of shapes.
- - It does not describe an API.

2/ http://w3c.github.io/data-shapes/semantics/Axiomatic

This document contains an axiomatic semantics for the core in 1/ above.

Significant Features:
- - It provides a formal specification for a core of SHACL in terms of an
  axiomatization.
- - The core contains potentially recursive shapes, but not closed shapes or
  global constraints.
- - Some of the low-level portions are under-specified.
- - It has errors.
- - It is incomplete.
- - It does not match the description in 1/ above.

3/ http://w3c.github.io/data-shapes/shacl/

This document contains a formal specification of SHACL based on SPARQL with
extra functionality.

Significant Features:
- - It provides a formal specification for SHACL in terms of an extended
  version of SPARQL.
- - It presents a full SHACL (modulo some of the non-validation portions).
- - Its version of SHACL has all the expressive power of SPARQL.
- - Its version of SHACL permits global constraints and recursive shapes but
  not closed shapes.
- - It provides a macro-expansion language.
- - It provides violation reporting.
- - The specification of recursive shapes appears to be ill-founded.
- - It does not define a core, but the high-level constructs can act as such.
- - The core does not need to be implemented using a SPARQL engine.
- - It defines several methods for controlling evaluation of shapes.
- - It defines a limited API.

4/ https://www.w3.org/2014/data-shapes/wiki/Shacl-sparql

This document contains a formal specification of SHACL directly based on
SPARQL.

Significant Features:
- - It provides a formal specification for SHACL in terms of SPARQL.
- - It presents a full SHACL (modulo some of the minor features and some of
  the non-validation portions).
- - Its version of SHACL has all the expressive power of SPARQL.
- - Its version of SHACL permits global constraints but not recursive shapes
  or closed shapes.
- - It provides violation reporting.
- - It does not define a core, but the high-level constructs can act as such.
- - The core does not need to be implemented using a SPARQL engine.
- - It defines several methods for controlling evaluation of shapes.
- - It defines a flexible API.



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Received on Friday, 20 March 2015 00:03:43 UTC

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