It seems reasonable to also include the elem_type in the creation of new notions with parents.

I came across this when using add_instances(), as the use of a DataProperty created as a child of another DataProperty leads to erroneous behavior. Line 700 (if DataProperty in pred.is_a:) checks against the elem_type, which is currently only included for notions without parents. This seems to also apply to line 710. Predicates, that are created as children of other predicates, simply lack the DataProperty or ObjectProperty parent, which is required to evaluate the conditions (l.700, l.710) to true.

Here is a minimal example:

base_classes = [["foo", None],]
base_dps = [["has_value", None, True, None, None, None, None, None, None, None],
            ["has_string_value", "has_value", True, None, None, None, None, None, None, None],]
base_instances = [["bar", "foo", "has_string_value", "baz", "string"],]

Adding the instance currently results in pred.is_a [base.has_value, owl.FunctionalProperty] instead of the required [base.has_value, owl.DatatypeProperty, owl.FunctionalProperty].