[SPIN] Overriding spl:Arguments in subclasses

[Martynas Jusevicius]

Hey,

I have a somewhat artificial use case where both a class and its superclass each have an spl:Argument with the same predicate, but different spl:defaultValue, and possibly other properties:

    :Template a spin:Template ;
        spin:constraint [ a spl:Argument ;
            spl:predicate :property ;
            spl:valueType xsd:long ;
            spl:defaultValue 111
        ] .

    :SubTemplate a spin:Template ;
        rdfs:subClassOf :Template ;
        spin:constraint [ a spl:Argument ;
            spl:predicate :property ;
            spl:valueType xsd:long ;
            spl:defaultValue 999
        # spl:optional true
        ] .

When [ a :SubTemplate ] is instantiated, what will be its :property value (assuming it comes from spl:defaultValue)?

I would think the subclass argument has precedence, but looking at the ModuleImpl code, it seems that a List<Argument> is collected from the class and all its superclasses, ignoring inheritance:
https://github.com/TopQuadrant/shacl/blob/master/src/main/java/org/topbraid/spin/model/impl/ModuleImpl.java

But maybe the inheritance/precedence is handled somewhere else?

Also, would it be illegal for the subclass to define the argument as spl:optional if the superclass does not do so? Wouldn't that break the template contract? I guess the same applies to redefinition of spl:valueType etc.

Thanks,


Martynas
atomgraph.com

[Holger Knublauch]

Hi Martynas,

as you have found out, this scenario is not supported by SPIN. Multiple declarations of the same predicate lead to undefined behavior. I am not particularly keen to touch this area of code, because it is so widely used and I don't want to risk regression bugs or performance degradation at this stage. Given that this doesn't appear to be a common scenario, your work-around is to not declare the argument twice, for example by having an abstract superclass for both templates, where only the subclasses declare :property.

Holger

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[Martynas Jusevicius]

Thanks Holger.

I think a solution could be to have 2 sets of arguments: template-local (by default), and inheritable (defined so explicitly), or "tunneled". Subclasses would not see the local arguments of superclasses, and it would be an error to redefine tunneled arguments with a different contract.

This is the idea behind tunnel parameters in XSLT 2.0: https://www.w3.org/TR/xslt20/#tunnel-params