Both specialisation and generalisation are useful techniques for developing superclass/subclass relationships. The uses of specialisation or generalisation technique for a particular situation depends on the following factors:
Nature of the problem.
Nature of the entities and relationships.
The personal preferences of the database designer.
Specialisation is the process of identifying subsets of an entity set (the superclass or supertype) that share some distinguishing characteristic. In other words, specialisation maximises the differences between the members of an entity by identifying the distinguishing and unique characteristics (or attributes) of each member. Specialisation is ...