BPDMF2 — representation of multiple inheritance

The representation of multiple inheritance prevents from using XSD extension mechanism. As a results, it is impossible to serialize properties which have an abstract type, the sub-type of which having multiple super-type. This is a major issue as it prevents from building a proper, sharable XSD stack.

1. Apply org.omg.xmi.useExtension=true to top package
2. Use the folowing multiple inherintance algorithm for XMI serialization

A. The mainSuperType tag is taken into account only at one level.
B. Properties coming from the main super-type and its hierarchy (without distinguishing between main or not main super-types) are not copied.
B. Properties coming from the other super-types and their super-type hierarchy (without distinguishing between main or not main super-types) are copied expect for those properties that comes from classes that are also in the main-super type hierarchy (see previous).