[Otlet] wanted to penetrate the boundaries of the books themselves, to unearth the “substance, sources and conclusions” inside. Taking the Dewey Decimal system as his starting point, Otlet began developing what came to be known as the Universal Decimal Classification, now widely recognized as the first—and one of the only—full implementations of a faceted classification system. While Ranganathan rightly receives credit as the philosophical forbear of facets, Otlet was the first to put them to practical use.