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Libraries at Rensselaer Polytechnic Institute

Deciphering Call Numbers: Call Numbers

The RPI Libraries use two distinct kinds of call number classification systems: Library of Congress and Dewey Decimal.

The Library of Congress Classification (LCC) system was developed at the turn of the 20th century and was specifically created to categorize books and other items held in the Library of Congress. It features 21 primary subject categories which are identified by letters of the alphabet. The letters I and O are not used because of their similarity to the numbers one (1) and zero (0), and the letters W, X, and Y have been reserved for future use. This is the main classification system used at the RPI Libraries, and is the scheme commonly used in academic libraries.

The Dewey Decimal Classification (DDC) system was developed in 1876 as a means of organizing all knowledge. The DDC uses notation in Arabic numerals, well-defined categories, well-developed hierarchies, and a rich network of relationships among topics. The ten basic classes, beginning with 000 and ending with 999 are organized by disciplines or fields of study, where each set of hundreds (100, 200, etc.) represents different fields. Each main class is further divided into ten divisions, and each division into ten sections. The DDC is customarily used in public libraries; however, RPI uses the DDC to arrange the journal collection at Folsom Library.

Call numbers can be thought of as a file path, and the library can be thought of as a large computer that you can browse on foot. For example, if you checked the RPI Libraries online catalog and found a book that you want to borrow, for instance “Lord of The Rings: The Two Towers” by J.R.R. Tolkien, you would first go to Folsom Library, then find the literature section (P) on the 3rd Floor, navigate to the English Literature section (PR), and locate the book (a.k.a. your file).  That particular file path would look something like "RPI:\Folsom Library\P\PR\PR6039. O32 L6 1965 pt.2."

Library of Congress Classification (LCC) System

Library of Congress Classification System's Main Categories

For an interactive list of categories and to search them more in depth, click  here.

Library of Congress main classification categories

Dewey Decimal Classification (DDC) Scheme

Dewey Decimal Classification System's Main Fields

For a further breakdown of the DDC main categories into its divisions, click here.

image of the Dewey Decimal Classification scheme