Issue 414: list constraints

[jeswr]

Closes #414. This PR implements sh:minListLength, sh:maxListLength and sh:uniqList.

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My interpretation of the following from the definition of 2.1.1 Constraints, Parameters and Constraint Components is that because the sh:MemberShapeConstraintComponent now has multiple parameters; there can only be one occurrence of sh:memberShape in a given shape - and I have updated the sh:maxCount accordingly.

Some constraint components declare only a single parameter. For example sh:ClassConstraintComponent has the single parameter sh:class. These parameters may be used multiple times in the same shape, and each value of such a parameter declares an individual constraint. The interpretation of such declarations is conjunction, i.e. all constraints apply. The following example specifies that the values of ex:customer have to be SHACL instances of both ex:Customer and ex:Person.

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This is currently targeted to #403 branch for a smaller diff in the GH UI. #403 should be merged and this targeted to gh-pages rather than merging this branch into #403

[HolgerKnublauch]

I think you have linked the new constraint parameters to the same constraint component for memberShape. I believe it would be better to introduce separate constraint components for each of them. It makes the definition more modular but, more importantly, it is perfectly sensible to use for example sh:minListLength without a sh:memberShape constraint.

[HolgerKnublauch]

I wouldn't worry too much about malformed lists. Usually people use tools to produce them, including editing TTL source code. So if they are reported twice, this shouldn't be the end of the world.

[jeswr]

I also saw a comment about lists not being valid objects of sh:targetNode but it's now not appearing in the GH UI - was this comment deleted because the statement doesn't hold, or is GH doing weird things?

[HolgerKnublauch]

Yeah my fault. I deleted the comment because I understood later what you did.

[jeswr]

I think this is good to go now - I suggest we merge this to gh-pages and close #403 as I have applied changes to the sh:memberShape definition in this PR including moving it to the new List Constraint Component section and addressing #416 (comment)

[HolgerKnublauch]

I am in the middle of implementing all this in Java and found various issues.

[jeswr]

I have addressed the issues found - is there an(other?) open source implementation that'd be useful for me to implement the changes against (@bergos' JS shacl-engine perhaps) in case there are any more errors to catch.

P.S. I am conferencing for the next 3 days so will be slow to respond