MPEG-21 Part 7: Digital Item Adaptation
Introduction to MPEG-21 
Today, many elements exist to build an infrastructure for the delivery and consumption of multimedia content. There is, however, no 'big picture' to describe how these elements, either in existence or under development, relate to each other. The aim for MPEG-21 is to describe how these various elements fit together. Where gaps exist, MPEG-21 will recommend which new standards are required. ISO/IEC JTC 1/SC 29/WG 11 (MPEG) will then develop new standards as appropriate while other relevant standards may be developed by other bodies. These specifications will be integrated into the multimedia framework through collaboration between MPEG and these bodies.
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.
Digital Item Adaptation Overview 
The goal of the Terminals and Networks key element is to achieve interoperable transparent access to (distributed) advanced multimedia content by shielding users from network and terminal installation, management and implementation issues. This will enable the provision of network and terminal resources on demand to form user communities where multimedia content can be created and shared, always with the agreed/contracted quality, reliability and flexibility, allowing the multimedia applications to connect diverse sets of Users, such that the quality of the user experience will be guaranteed.
The Digital Item Adaptation tools in this specification are clustered into seven major categories as illustrated in Figure 1. The categories are clustered according to their functionality and use for Digital Item Adaptation around the Schema Tools and Low-Level Data Types. The schema tools provide uniform root elements for all DIA descriptions as well as some low-level and basic data types which can be used by several DIA tools independently.:
The first major category is the Usage Environment Description Tools, which include User characteristics, terminal capabilities, network characteristics and natural environment characteristics. These tools provide descriptive information about these various dimensions of the usage environment, which originate from Users, to accommodate, for example, the adaptation of Digital Items for transmission, storage and consumption.
The second category is referred to as BSDLink which provides the facilities to create a rich variety of adaptation architectures based on tools specified within this part of ISO/IEC 21000, ISO/IEC 21000-2, and ISO/IEC 15398 among others.
Bitstream Syntax Description Tools comprise the third major category of Digital Item Adaptation tools. A BSD describes the syntax – in most cases, the high level structure – of a binary media resource. Using such a description, a Digital Item resource adaptation engine can transform the bitstream and the corresponding description using editing-style operations such as data truncation and simple modifications.
The fourth category of tools is referred to as Terminal and Network Quality of Service. The description tools specified in this category describe the relationship between QoS constraints (e.g., on network bandwidth or a terminal’s computational capabilities), feasible adaptation operations satisfying these constraints and associated media resource qualities that result from adaptation. This set of tools therefore provides the means to trade-off these parameters with respect to quality so that an adaptation strategy can be formulated and optimal adaptation decisions can be made in constrained environments.
The Universal Constraints Description Tool form the fifth category of tools which enables the possibility to describe limitation and optimisation constraints on adaptations.
The sixth category is referred to as Metadata Adaptability. This description tool specifies hint information that can be used to reduce the complexity of adapting the metadata contained in a Digital Item. On the one hand they are used for filtering and scaling and on the other hand for integrating XML instances.
For Session Mobility, the seventh category of tools, the configuration state information that pertains to the consumption of a Digital Item on one device is transferred to a second device. This enables the Digital Item to be consumed on the second device in an adapted way.
Finally, the eighth category of tools are referred to as DIA Configuration Tools which provides information required for the configuration of an Digital Item Adaptation Engine.
A proposal of generic bitstream syntax description together with Siemens Munich. This approach enables resource format independent bistream synatx descriptions to be constructed . In December 2003 we reached Final Draft International Standard  stage (including our contribution:-).
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References and Public Documents
Jan Bormans, Keith Hill , MPEG-21
Overview v.4, doc. N5231, Shanghai, China, October 2002