PySHACL's flaw with regard to "targetObjectsOf" or our misunderstaning? about pyshacl HOT 8 CLOSED

Hi @xyzisinus,
Thanks for your detailed write-up of this report.

I haven't yet had a chance to look deeply into what is causing the problem you are seeing, but my immediate concern is it might be related to some changes introduced in the most-recent v0.11.3 release of pyshacl.

Have you tried any other versions other than the latest release, to try to reproduce your problem?

Please try v0.11.1 to see if the problem is present, and if so, please try v0.10.0 and see if it is still present there.

I will look more deeply into exactly what is causing this problem later this weekend.

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Update, reading it again, I think I see a problem in your shape definition. You are using both sh:targetObjectOf and sh:property together in the same shape, to try to enforce the same rule in two different ways. That is saying "everything that is an object of this property, should also have this property at this property path" which is incorrect for what you are trying to achieve.

You can do this rule with sh:targetObjectOf or sh:property but not both.

Try this:

schema:AddressShape
    a sh:NodeShape ;
    sh:targetObjectsOf schema:hasAddress ;
    sh:class schema:PostalAddress .

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Update 2:
I was just thinking, you might be confusing targetObjectsOf and targetSubjectsOf
For example, changing your Shape to this, will work:

schema:AddressShape
    a sh:NodeShape ;
    sh:targetSubjectsOf schema:hasAddress ;
    sh:property [
        sh:path schema:hasAddress ;
        sh:class schema:PostalAddress ;
    ] .

That will do what you want, is it saying "get all targets that are subjects which have this hasAddress" and "on those targets, follow this property path to check its class".

However using targetObjectsOf like this:

schema:AddressShape
    a sh:NodeShape ;
    sh:targetObjectsOf schema:hasAddress ;
    sh:class schema:PostalAddress .

this is easier, and shorter and identical to the above. It says "find all targets which are the object of hasAddress, and check its class."

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@ashleysommer Thank you very much for your quick response! I tried both suggestions in your update 2. The result of the first suggestion:

Constraint Violation in ClassConstraintComponent (http://www.w3.org/ns/shacl#ClassConstraintComponent):
        Severity: sh:Violation
        Source Shape: [ sh:class schema:PostalAddress ; sh:path schema:hasAddress ]
        Focus Node: ex:Bob
        Value Node: ex:Alice
        Result Path: schema:hasAddress

The result of the second suggestion (2 errors reported):

Constraint Violation in ClassConstraintComponent (http://www.w3.org/ns/shacl#ClassConstraintComponent):
        Severity: sh:Violation
        Source Shape: schema:AddressShape
        Focus Node: ex:Alice
        Value Node: ex:Alice
Constraint Violation in NodeConstraintComponent (http://www.w3.org/ns/shacl#NodeConstraintComponent):
        Severity: sh:Violation
        Source Shape: [ sh:node schema:AddressShape ; sh:path schema:address ]
        Focus Node: ex:Bob
        Value Node: ex:BobsAddress
        Result Path: schema:address

Out of these two alternatives, the first one makes more sense to me because "hasAddress" path is used in reasoning.

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And I'm still bit confused looking at the code in https://github.com/RDFLib/pySHACL/blob/master/pyshacl/shapes_graph.py starting from line 187, especially line 189 where targetObjectsOf is concerned. In this chunk of code (till the end of the file) I don't see how targetObjectsOf gets to participate in finding the focus nodes which are objects of some shape. I haven't looked/poked the code carefully yet. My observation is just from a quick scan of the code. Thanks!

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Hi, the chunk of code in that file you're looking at is the "shapes detection routine" its job is to find all possible permutations of SHACL shapes in a shapes file, in order to later iterate over them. The code which builds focus nodes for a given shape is in a different file in the project.

See how sh:targetObjectsOf is used here:

Then look on line 175, 210, and 239. I know the code is hard to follow, but I hope that helps you to understand how sh:targetObjectsOf is done in PyShacl.

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@ashleysommer Thank you for the pointer! I'll look at the code when I get a chance :)

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@ashleysommer I'm closing the issue now. Thank you for your support and insight!

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