The document discusses the Dewey Decimal System created by Melvil Dewey in 1876. It divides books into 10 main categories, each represented by a 100s number. Dewey organized books by subject to make them easier for library patrons to find. The system uses a call number with shelf location information to allow efficient browsing. A story is told of Dewey showing an alien visitor how the classification system works by relating each 100s group to aspects of human knowledge and experience.