This International Standard specifies a metadata system for describing multimedia content. It specifies the Description Definition Language (DDL) that comprises part 2 of the standard (ISO/IEC 15938-2). The goal of this part of the MPEG-7 International Standard is to specify a language that will enable MPEG-7 users and developers to: - create valid MPEG-7 description schemes and descriptors; - develop tools such as editors and parsers for processing descriptions, description schemes and descriptors; - generate refinements, extensions and modifications to the DDL.