Re: Comments about the Concepts in the SHACL Document

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I agree that there needs to be some notion of the basics of SHACL and how
they work before substantive work can be done on the document.  Once this
foundation has been ironed out, it can be used to drive changes to the
document.  I was trying to go along the path suggested in the recent WG
resolution and am now convinced that it will not work.

Having a bunch of issues that are resolved one by one is also not going to
work as it is not going to produce a cohesive support for SHACL.

I was trying to put together a description of the required underpinnings of
SHACL.  Every time I tried I ended up getting pulled into details.  I'm now
trying to put together a very short description of a few basic principles
that can be used as a starting point for further work.

peter


On 05/29/2015 09:50 PM, Holger Knublauch wrote:
> Thanks, Peter. I believe before it's worth to address these issues, we
> first need a general agreement on the terminology, how the engine's outer
> algorithms work and how the top-level syntax looks like. Your own
> proposal uses Constraints and Shapes differently than mine, so it makes
> little sense for me to update the current draft if this gets rewritten
> anyway. I also look forward to your suggestion on how to restructure the
> whole document (from a parallel thread). Meanwhile I suggest we continue
> with the raised issues for a few weeks (which could easily turn into
> months).
> 
> Holger
> 
> 
> On 5/30/2015 6:09, Peter F. Patel-Schneider wrote: I read over
> https://w3c.github.io/data-shapes/shacl/ and noticed a bunch of problems.
> I have gathered these by concept and added some comments.
> 
> 
> Shape WRONG - "describes a group of constraints with the same focus
> node" WRONG - "is a group of constraints that have the same focus node" -
> Mentioning focus node at this level is incorrect. - Ignores scope aspect
> of shapes.
> 
> Closed Shape ? - closed shape as one of the "other shape-based
> constraints" - Is closed shape a constraint?
> 
> Scope AMBIGUOUS - "pre-conditions that must hold before a constraint is
> applied to a given focus node" - No notion of constraint application
> defined in document. - Scope is used on both shapes and constraints.
> 
> Class Scope - AMBIGUOUS - "apply to all instances of these linked
> classes" - What is an instance of a class?
> 
> Constraint WRONG - "a condition that can be validated against a graph" 
> WRONG - "defines restrictions on the structure of an RDF graph" - Most
> constraints are validated against a graph and a node in the graph. WRONG
> - "evaluated against a focus node" - Not for global constraints.
> 
> Global Constraint - Different from other constraints as they don't have a
> real scope.
> 
> Constraint Violation POOR NAME - violations of component constraints may
> not be an overall violation INCORRECT BEHAVIOUR - violations of component
> constraints are reported, even for OR and NOT UNSPECIFIED BEHAVIOUR -
> constraints with components only specify how to handle errors INCOMPLETE
> - no way of producing different kinds of violations in high-level 
> language
> 
> Template INCOMPLETE - no connection betweeen query results and
> violations
> 
> Supported Operations INCORRECT - validateConstraint needs a focus node
> for most constraints BADLY SPECIFIED - validateNodeAgainstShape ignores
> shape scope BADLY SPECIFIED - validateNode ignores some kinds of scopes 
> BADLY SPECIFIED - validateGraph ignores some kinds of scopes -
> validateGraph does not handle global constraints
> 
> 
> Missing: - a firm definition of RDF graphs that encode valid SHACL
> constructs - e.g., optionality of various parts of property constraints -
> an integrated definition of how SHACL works
>> 
> 
> 
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Received on Saturday, 30 May 2015 12:52:14 UTC