The following changes have been done in the Metamodel in order to manage
the Type of Parameter.
1. Replaced IFML:NamedElement with IFML:IFMLNamedElement inheriting from
UML2: NamedElement. IFMLNamedElement provides the implementation of the
methods generated from UML. 
2. Replaced the relationship between Slot, Field  and Parameter as
Inheritance. Field and Slot inherit from Parameter