In the current phase of work DAVIC is concentrating on digital audio-visual applications and services of broadcast and interactive type and Fig. 2 is a very general representation of the system being addressed. It comprises 5 entities: the content provider system, the service provider systems and the service user system; the three entities being connected by two entities - delivery systems - the first connecting the content provider to the service provider and the second the service provider to the service user.
As a rule DAVIC specifications contain normative and informative parts. Normative parts have to be implemented as in the specifications in order to claim conformity of a subsystem to DAVIC specifications. Informative parts are included as well for the purpose of clarifying the normative parts of the specifications and to give general assistance to implementers of specifications.
DAVIC specifications contain the reference model of the DAVIC system and its subsystems. DAVIC specifications also define reference points, i.e. points of particular interest in the system. These points have a normative value if they are accessible. Therefore a digital audio-visual subsystem conforms to DAVIC specifications if its accessible reference points do. This means that a subsystem can be considered as a black box and DAVIC specification conformity is only assessed at the external reference points.
DAVIC specifications define the technical "tools" whose use allows the provision of "functionalities" required by the DAVIC system and the applications that make use of it. Tools are usually associated with grades that determine the level of performance of a given tool, e.g. mono-stereo-multichannel audio, TV-HDTV, bandwidth of a return channel etc.
DAVIC specifications are issued in versions: DAVIC 1.0, DAVIC 1.1 etc. The current DAVIC 1.0 version of specifications defines a first set of tools enabling the deployment of systems that support initial applications such as TV distribution, near video on demand, video on demand and some basic forms of teleshopping. Each future version will specify different grades of previously defined tools or more tools in addition to previously specified tools.
Even if DAVIC defines only one tool per functionality the toolkit nature of DAVIC specifications would lead to too many incompatible instantiations of subsystems. It is therefore necessary to define groupings of tools with associated grades which are deemed to have a particular value in the application domain. These serve as a guidance to manufacturers and application providers, are called profiles and have normative value.
DAVIC specifications are developed by making use of the best available technologies or combinations thereof and as far as feasible are validated by technical interoperability tests. Because of the toolkit nature of the specifications, however, no claim can be made as to the suitability of DAVIC specifications or of any of its parts for any intended purpose of a user.
As a rule DAVIC specifications are accompanied by documents specifying methods to test the conformity of reference points to the specifications.
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