There are two main types of library classification systems: The Dewey Decimal and Library of Congress. Both use similar classes that documents are placed under, but they are different enough that they cannot be used interchangeably. The call numbers of each system are a combination of letters and numbers that indicate what class the document belongs to and who authored it. These classifications are placed on the bottom of the books' spines.
The Dewey Decimal and Library of Congress systems share 10 divisions that break down into subdivisions for more specific categorizations. These include generalities, philosophy and psychology, religion, social science, language, natural science and mathematics, technology and applied science, art, literature and geography and history. The Library of Congress system has additional divisions: sciences of history, general and old world history, geography, anthropology, recreation, political science, law, education, music, medicine, agriculture and
military and naval science.
This system primarily appears in elementary, secondary and public libraries. It is named after its creator, Melvil Dewey. The first line in the call number has numbers and decimals that identify the work's general division and its specific subdivision. The second line is called the cutter line. It has a combination of letters and numbers linked to the author's name.
This system is one of the most widely used and frequently appears in university libraries. The first and second lines of a call number are held by two letters and four numbers that indicate the subject of the book. The first letter in this line is the class. The second letter is the subclass. The third line gives the first letter of the author's name, followed by a set of numbers that are linked to the author's name. The fourth line is the year of publication.