1. According to Fowler's definition this pattern is implemented by having all classes in a layer inherit from a superclass. But after some googling it appears all of the following are considered as implementations of a Layer Supertype pattern:
a - all classes in a layer inheriting from the same superclass
b - having only some ( thus not all ) of classes in a layer inheriting from a superclass
c - layer having superclasses S1 and S2, where classes A and B inherit from S1, while C inherits from S2
So which of above are considered as implementations of a Layer Supertype?
2. If a,b and c are all considered implementations of a Layer SuperType, then I fail to see how this pattern is any different from a regular class inheritance. In other words, couldn't we then claim we're using Layer Supertype any time some class inherits from another class?