该国际标准规定了用于描述多媒体内容的元数据系统。它规定了构成标准（ISO/IEC 15938-2）第2部分的描述定义语言（DDL）。MPEG-7国际标准这一部分的目标是指定一种语言，使MPEG-7用户和开发者能够:？创建有效的MPEG-7描述方案和描述符；？开发工具，如编辑器和解析器，用于处理描述、描述方案和描述符；？生成对DDL的细化、扩展和修改。本国际标准描述了DDL的特征。它定义了DDL构造和数据类型的语法，并提供了可选的（信息性的）示例，这些示例说明了DDL在MPEG-7描述的规范和实例化中的应用。

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.

This International Standard describes the features of the DDL. It defines the syntax of the DDL constructs and datatypes and provides optional (informative) examples that illustrate the application of the DDL to the specification and instantiation of MPEG-7 descriptions.