ISO/IEC 21000-2:20 05规定: 模型:数字项目声明模型描述了一组抽象的术语和概念，以形成定义数字项目的有用模型。表示:数字项目声明语言（DIDL）基于上述模型中定义的术语和概念。它包含每个DIDL元素的语法和语义的规范性描述，如XML所表示的。模式:信息丰富的XML模式，说明了在符合规范表示的XML中表示DID的完整语法。详细示例:提供了DIDL文档的说明性（非规范性）示例，以帮助理解规范的使用及其潜在应用。 ISO/IEC 21000(MPEG-21)系列国际标准定义了多媒体传送和消费的开放框架，内容创建者和内容消费者都是焦点。MPEG-21的愿景是定义一个多媒体框架，以实现跨不同社区使用的广泛网络和设备透明和增强地使用多媒体资源。 MPEG-21(ISO/IEC 21000-2:20 05)的第二部分规定了用于声明数字项目的结构和组成的统一和灵活的抽象和可互操作的表示。数字项目声明（DID）涉及指定数字项目的资源、元数据及其相互关系。DID是使用数字项目声明语言（DIDL）完成的。

ISO/IEC 21000-2:2005 specifies:

• Model: The Digital Item Declaration Model describes a set of abstract terms and concepts to form a useful model for defining Digital Items.
• Representation: The Digital Item Declaration Language (DIDL) is based upon the terms and concepts defined in the above model. It contains the normative description of the syntax and semantics of each of the DIDL elements, as represented in XML.
• Schema: Informative XML schemas illustrating complete grammars for representation of the DID in XML conforming to the normative representation.
• Detailed Examples: Illustrative (non-normative) examples of DIDL documents are provided to aid in understanding the use of the specification and its potential applications.

The ISO/IEC 21000 (MPEG-21) series of International Standards defines an open framework for multimedia delivery and consumption, with both the content creator and content consumer as focal points. The vision for MPEG-21 is to define a multimedia framework to enable transparent and augmented use of multimedia resources across a wide range of networks and devices used by different communities. This second part of MPEG-21 (ISO/IEC 21000-2:2005) specifies a uniform and flexible abstraction and interoperable representation for declaring the structure and makeup of Digital Items. A Digital Item Declaration (DID) involves specifying the resources, metadata, and their interrelationships for a Digital Item. A DID is done using the Digital Item Declaration Language (DIDL).