A useful tool which is used for specifying the logical properties of a data type is called the abstract data type or ADT. The term "abstract data type" refers to the fundamental mathematical concept which defines the data type. In defining ADT as a mathematical concept, we are not concerned or worried about space or time efficiency.
An ADT comprises of two parts:- which are value definition and operator definition. The value definition defines the collection of the values for the ADT and contains two parts: one is definition clause and the other is condition clause. For example, the value consist definition for the ADT RATIONAL states that a RATIONAL value contains two integers, the second of which is not equal to 0. We apply array notation to indicate the parts of an abstract type.