The MPEG-7 standard, formally named "Multimedia Content Description" aims to be an overall for describing any multimedia content. MPEG-7 standardizes so-called "description tools" for multimedia content: Descriptors (Ds), Description Schemes (DSs) and the relationships between them. Descriptors are used to represent specific features of the content, generally low-level features such as visual (e.g. texture, camera motion) or audio (e.g. melody), while description schemes refer to more abstract description entities (usually a set of related descriptors). These description tools as well as their relationships are represented using the Description Definition Language (DDL), a core part of the language.
The W3C XML Schema recommendation has been adopted as the most appropriate schema for the MPEG-7 DDL, adding a few extensions (array and matrix datatypes) in order to satisfy specific MPEG-7 requirements. MPEG-7 descriptions can be serialized as XML or in a binary format defined in the standard.