DDL (Description Definition Language) is part of the MPEG-7 standard. It gives an important set of tools for the users to create their own Description Schemes (DSs) and Descriptors (Ds). DDL defines the syntax rules to define, combine, extend and modify Description Schemes and Descriptors.
DDL is not a modeling language, such as the Unified Modeling Language (UML), but a schematic language to represent the audiovisual data results, which must conform to the descriptors, the description schemes and the MPEG-7 descriptions.
MPEG-7 DDL Must:
In 1999, the team in charge of MPEG-7 DDL was comparing and evaluating proposals in the MPEG-7 AHG Test And Evaluation Meeting held in Lancaster. The main agreement was that DDL had to use the XML syntax, support object-oriented semantics, as well as being able to validate structural, relational and data typing constraints.
Although no proposal satisfied the requirements, the DSTC proposal was used as a starting point, extending it with the additions of ideas and components from other proposals and contributors. Moreover, the strategy was to keep tracking and influencing the W3C community, specially the XML Schema, XLink, XPath and XPointer working groups.
At the 51st MPEG meeting, the adoption of the XML Schema syntax with specific MPEG-7 extensions was decided.
As defined in the MPEG-7 requirements document:
They are basic to satisfy the MPEG-7 DDL requirements