an organized structure for arranging or classifying

a system used by libraries to classify nonfictional publications into subject categories; the subject is indicated by a three-digit numeral and further specification is given by numerals following a decimal point; publications are shelved by number

a classification system where entries are arranged based on some hierarchical structure

a system of classifying into files (usually arranged alphabetically)

a system for classifying things into groups

a system of classifying according to quality or merit or amount