Usually the process of classification involves the use of established classification system
. Numerical and alphanumerical systems are created for library uses. Such notations given to each item in the library will improve the chances of identifying them easily in the cluster.
Among the classification systems used in libraries, two are most prominent. First one is the Dewey decimal classification or the DDC system and the second one is the Library Congress or LC classification system. While the former is based on numerical breakdown of the topics, the second one is made of alphanumerical subject organization.