Roles with multiple superclasses lead to duplicate membership objects

[alexdutton]

The President of Brazil has two superclasses: head of government, and president. The superclasses have disjoint inheritances, so we can't exclude one for being in the inheritance graph of the other.

At the moment our executive query returns multiple sets of bindings, one for each role superclass. We need a way to pick the more sensible of the two, and only output one membership object.

This problem may also apply to legislative roles.

[crowbot]

I guess another option here is to allow more than one role_superclass element, although I'm not sure how meaningful that would be.

[crowbot]

Decide what to do about roles with multiple role superclasses