ISO/IEC 21000 (MPEG-21) 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.
The basic architectural concept in MPEG-21 is the Digital Item. Digital Items are structured digital objects, including a standard representation and identification, and metadata. They are the basic unit of transaction in the MPEG-21 framework. Many MPEG-21 applications have the requirement to uniquely identify Digital Items.
ISO/IEC 21000-3:2003 provides a simple but flexible mechanism to:

• Uniquely identify Digital Items and parts thereof (including resources);
• Uniquely identify IP related to the Digital Items (and parts thereof), for example abstractions;
• Uniquely identify Description Schemes;
• Use identifiers to link Digital Items with related information such as descriptive metadata (non-normative).

The DII specification does not specify new identification systems for the content elements for which identification and description schemes already exist and are in use.
Identifiers covered by this specification can be associated with Digital Items by including them in a specific place in the Digital Item Declaration (ISO/IEC 21000-2).