ISO/IEC 13522 specifies the coded representation of multimedia/hypermedia information objects (MHEG objects) for interchange as final form units within or across services and applications, by any means of interchange including local area networks, wide area telecommunication or broadcast networks, storage media, etc.

MHEG objects can be produced by computer tools taking as source form multimedia applications designed using multimedia scripting languages. In this context, the MHEG script (or program) classes are intended to complement the other MHEG classes in expressing the functionality commonly supported by scripting languages. Script (or program) objects express more powerful control mechanisms and describe more complex relationships among MHEG objects than can be expressed by MHEG action and link objects alone. Furthermore, script (or program) objects express access to and interaction with external services provided by the run-time environment.

ISO/IEC 13522-5 defines the MHEG object classes for interchange and use in base-level applications intended to be run on limited resource terminals such as set-top-boxes in such contexts as interactive broadband services.

ISO/IEC 13522-5 defines the coded representation for program objects in an open manner so that program objects may encapsulate either standardised or proprietary program code. ISO/IEC 13522-5 allows program objects to include or reference programs that may be encoded in any encoding format as defined by the application domain.

The scope of this part of ISO/IEC 13522 is to define the semantics and final-form coded representation for the interchange of enhanced interactive multimedia applications.

These applications extend applications covered by ISO/IEC 13522-5 in incorporating functionality such as computing (data processing) and extended communication with the external environment, including servers, local devices, etc.

These applications may be exploited in any communication environment including broadcast-only mode, interactive client-server or peer-to-peer (conversational). However, the main focus is on interactive retrieval (client-server) applications running on limited resource set-top-units involving asymmetrical data interchange with real-time audiovisuals on the downstream channel.

The coded representation defined by this part of ISO/IEC 13522 specialises the coded representation defined by ISO/IEC 13522-5. Especially, this part of ISO/IEC 13522 defines the coded representation for the OriginalContent attribute of the MHEG-5 InterchangedProgram class. In addition, this part of ISO/IEC 13522 defines the Applet class; this subclass of InterchangedProgram features the ability to manage its own display and interaction, by delegation from the engine.

The resulting coded representation is

• compatible with that defined by ISO/IEC 13522-5;
• appropriate for execution on a set-top-unit with the same minimal resource constraints as expressed by ISO/IEC 13522-5.

This part of ISO/IEC 13522 specifies

• the interchange format for the OriginalContent attribute of the MHEG-5 InterchangedProgram class;
• the semantics of this coded representation;
• the coded representation and semantics of the Applet class;
• the semantic extensions to the MHEG-5 engine behaviour described by ISO/IEC 13522-5;
• the semantic restrictions on the MHEG-5 interchange format described by ISO/IEC 13522-5;
• the MHEG-5 API, which allows the code of an InterchangedProgram object to call upon the MHEG-5 engine's presentation functionality;
• the provisions for interworking between the MHEG-5 engine execution model and the execution model that underlies the program content interchange format.

MHEG engines are system or application components that handle, interpret and present MHEG objects. This part of ISO/IEC 13522 specifies the semantics of the MHEG-6 coded representation. These semantics are defined in terms of minimum requirements on the behaviour of MHEG-6 engines.

This part of ISO/IEC 13522 is applicable to all applications that interchange multimedia and hypermedia information.