1.4 Underlying Design Rationals

Having identified the class of systems to be captured by the model, let's turn our attention to the general guidelines which have driven our design decisions:

• Adequate modularization
  To facilitate the development and comparison of practical large-scale systems, the reference model must comprise a modularization of a generic process for multimedia presentation generation. Idealy, this modularization breaks down the generation process into logically distinct and computationally feasible subtasks.
  

• Appropriate degree of abstraction
  The reference model should, on the one hand, reflect the unique characteristics of multimedia generation. On the other hand, it should be general enough to capture the whole class of IMMPSs. Certainly, the generic architecture should abstract from concrete implementations, as it is always possible to rely on different mechanisms to accomplish a single generation subtask, and different formats to represent knowledge.
  

• Identification and classification of knowledge sources
  As intelligent presentation design is a knowledge intensive task, the reference model should exhibit the basic set of logically distinct knowledge sources which are required for multimedia presentation generation. The reference model should also make clear how processes and knowledge sources are related to each other. In particular, private knowledge sources, i.e., sources for which a single owner component can be located, should be distinguished from those sources which are shared among several components.
  

• Modeling of shared sources in the client-server paradigm
  To facilitate sharing of knowledge sources (in the generic architecture as well as in concrete system implementations) the latter should be modeled following the client-server paradigm. Such sources will be referred to as expert modules; they are deemed to serve requests from client modules, possibly belonging to other systems.
  

• Openness to other standards
  Multimedia generation comprises subtasks which have been treated in other disciplines. Therefore, the model should be open to combine with existing or potential standards in these disciplines. For example, the Computer Graphics Reference Model [3] may be used to instantiate the subcomponent for graphics generation in the generic architecture of our model. Moreover, the work described here has been strongly influenced by the PREMO [4] standardization initiative, as the PREMO results may be used for the description of generated multimedia presentations. Also one may rely on a standardized language for the exchange of knowledge between components, such as KQML (Knowledge Query and Manipulation Language [5]). Vice versa, the reference model can itself become a component of a superordinate model, such as the Seeheim Model (cf. 1.2).