The BBC's Lonclass ("London Classification") is a subject classification system used internally at the BBC throughout its archives. Lonclass is derived from the Universal Decimal Classification (UDC), itself a reworking of the earlier Dewey Decimal Classification (DDC). Lonclass dates from the 1960s, whereas UDC was created from DDC in the late 19th century. The BBC adaptation of UDC preserves the core features that distinguish UDC from DDC: an emphasis on a compositional semantics that allows new items to be expressed in terms of relationships between known items.