When the Evidence Interfaces are implemented by evidence entities, the methods defined by these interfaces will be implemented by those entities. These methods will of course be non-modeled so will only exist on the evidence entity impl classes. In order to access the non-modeled functions, it's necessary to cast from the impl class. Examples of this can be seen in the entity program listings later in section 3.2 of this document. This casting mechanism will not work though unless the factory class is extending the impl class as opposed to the base class. The only way that this can be achieved, if no non-stereotyped functions are being added to the class, is to add a non-stereotyped dummy function. If this is not done, it will result in a runtime error when the casting is executed.