A library classification is a system by which library materials are arranged according to subject. Library classifications use a notational system that represents the order of topics in the classification and allows items to be stored in that order. Library classification systems group related materials together, typically arranged in a hierarchical tree structure. A different kind of classification system, called a faceted classification system, is also widely used which allows the assignment of multiple classifications to an object, enabling the classifications to be ordered in multiple ways. The library classification numbers can be considered identifiers for resources but are distinct from the International Standard Book Number (ISBN) or International Standard Serial Number (ISSN) systems, which are unique commercial product identifiers.Today many classification schemes are available i,e, DDC, CC, UDC.