Abstraction:

Abstract datatypes are a part of the Object Oriented concept known as abstraction. It is the conceptual existence of classes within a database. A structural existence of the abstract kinds is enough. The methods attached to each level of abstraction might be called from the higher levels of abstraction.

Let consider an example where HOME APPLIANCES refers to a class of data. An "Electronic" is a subclass of the abstract class Home Appliances. The relationship among the new abstract class "Home Appliances" and the subclass "Electronic" would be known as a supertype to subtype relationship in the logical model of a relational database. The class "Home Appliances" is an abstract class, it has no actual example of objects in it.  It exists to define common features which pertain to all Home Appliances which is not only Electronic.