General Info on Dewy Decimal System - Most library users know the general structure of Melvil Dewey's decimal classification. First published in 1876, the Dewey Decimal Classification (DDC)* divides knowledge into ten main classes, with further subdivisions. More than 200,000 libraries in 135 countries use the Dewy Decimal System to organize their book collections. Its simple and logical framework is based on the principle of decimal fractions as class marks, which are expandable to make further subdivisions.