The user of any SET implementation should not be able to distinguish it from any other implementation based on its functional behavior. As far as the user can tell, the operations act like operations on the mathematical ideal of a set. A method without body (no implementation) is known as abstract method. A method must always be declared in an abstract class, or in other words you can say that if a class has an abstract method, it should be declared abstract as well.
Describe the role of indexing and abstracting in subject access and information retrieval.
Describe and apply the range of indexing and abstracting methods available for books, periodical literature, creative works, and online materials.