General guidance on using AQL to query taxonomies

[contranton]

Hi all,

I'm playing around talking to SysON via its GraphQL API and using AQL queries to access the model's contents. I'm a noob with EMF and OCL in general, so this might be super easy and I just missed it.

I want to do something like the following, to get all model elements which subtype from a given supertype:

aql:self.eResource().getContents().eAllContents(sysml::PartDefinition)
->select(c | c.oclIsKindOf( MySuperAmazingSupertype ))

which works when the argument of oclIsKindOf is directly qualified from the sysml EPackage, but not when it's a model element in my library -- in fact, I can't find the way to get AQL to recognize elements from my model or a user library in the query itself. Is there some EPackage like libraries I should be using?

I've also tried navigating sysml::Subclassification relationships. I've tried

aql:self.eResource().getContents().eAllContents(sysml::Subclassification)
->select(s | s.target.name = 'The Name of my super amazing supertype')
->collect(s | s.source)

but this doesn't seem to work due to reasons that escape me. It's weird since

...
->collect(s | s.target)
->collect (t | t.name)

shows me the correct name I want to select by, but then I can't dereference the source element.

Has anybody had success with something similar? I appreciate any and all help.

[gdaniel]

Hi,

Thank you for using SysON!

SysON does not consider your own Definition instances as types. This would require a bridge of some sort between EMF metamodels and SysML models, and we don't have this feature at the moment.

As a workaround, you can select the MySuperAmazingSupertype using its name.

aql:self.eResource().getContents().eAllContents(sysml::PartDefinition)->select(c | c.name = 'MySuperAmazingSupertype')

Looking at your second query, the key here is that Relationship#source and Relationship#target return lists of elements. As a result, s.target.name does not return a single name, but a list containing one name, and you cannot compare it as is with a string.

You can get the result you want by updating your query as follows:

aql:self.eResource().getContents().eAllContents(sysml::Subclassification)
  ->select(s | s.target->first().name = 'MySuperAmazingSupertype')
  ->collect(s | s.source->first())

Note that the query view in SysON indicates whether a result is a collection or not, but I have to admit it is not easy to spot at first sight.

As a side note, you can check the AQL documentation if you need some additional information on the language.

[contranton]

Thanks! That ->first() fix gives me the objects I was expecting.

I take it that with the current limitations it's not yet possible to recursively navigate the Subclassification tree to query for deeper levels of inheritance, at least with a single AQL query. Correct?

I can search by qualified name but it only works for finding containment, but not so much for inheritance. And using eInverse() I can start from my desired base class but finding all leaf elements requires me to know the depth a-priori.

For clarity, I mean that given something like

part def A;
part def AA :> A;
part def AAA :> AA;

part my_a : AAA;

I may query "Give me all PartUsages that eventually trace back to A"

[gdaniel]

I don't think it is doable indeed.
There are maybe some ways to compute a transitive closure in AQL but I don't see how at first sight.

It would be easier to create and register a service you can call from your query instead of relying on pure AQL:

aql:self.getAllRelatedPartUsages()

This can be achieved by implementing IInterpreterJavaServiceProvider

[gdaniel]

For the record, I found a pure AQL way to achieve what you want. It relies on the Type#allSupertypes() operation, which performs the kind of transitive closure (on super types) I was looking for.

I put below the query, I extracted the key parameters so you can easily tune it to your needs. Note that while in this special case it was possible to create a pure AQL implementation of this query, I still don't think there is a way to compute transitive closure in AQL, and as such I'd recommend to use a Java service to handle such queries.

aql:let superTypeToLookFor = 'AA' in
  let resultType = sysml::PartUsage in
    let subtypes = self.eResource().getContents().eAllContents(sysml::Type) in 
      subtypes->select(s | s.allSupertypes()->select(superType | superType.name = superTypeToLookFor)->notEmpty())
        ->filter(resultType)