The Dewey Decimal Classification (DDC), colloquially known as the Dewey Decimal System, is a library classification system that allows books to be put into their most appropriate location in a library using their subject as a sorting criterium.
It was first published by Melvil Dewey in 1876. During the years the system passed through 23 major editions, the latest printed in 2011.

So, having spent literally months if not years in libraries, and having managed a couple, the DDC is a well-known subject. The system has some background issues in the way certain topics are classified, but it is widely considered a good standard
As said it organizes library materials by putting them into ten classes, each of them divided into ten divisions, each of them having ten sections. The system’s notation uses Arabic numbers, with three integer numbers for the main classes and sub-classes, while decimals designate further divisions.
The structure of Dewey’s classification is hierarchical and the notation follows the same hierarchy.
So, if you are looking for a book in a library that uses the DDC, you should search for its Call Number
The Call Number works like an address: it tells us where the book is located in the library by giving you the class, the division, and the section of its classification.
The ten classes as described in the last revision are:
000 – Computer science, information, and general works
100 – Philosophy and Psychology
200 – Religion
300 – Social sciences
400 – Language
500 – Pure Science
600 – Technology
700 – Arts and Recreation
800 – Literature
900 – History and Geography
Should you decide to manage a library using Open-Source Software, I recommend the two I used most frequently and with more satisfaction: Evergreen and Opals.
If you need help in setting up, managing, or designing the services and offers of a library, contact me!