An important task of an IMMPS is the transformation of media communicative acts into specifications of media objects together with a specification of an overall presentation layout. While it might seem straightforward just to have two layers in the RM, say one for the production of media objects and a subsequent one for the presentation layout, we have adopted another specification which is based on the following observations:
The Media Design Component (cf. Fig. 7) can be regarded as the location where to plug in so-called media/mode-specific design components, i.e., dedicated modules for designing 2D- and 3D graphics, natural language utterances, animation, video, music etc. A Dispatching Component has been included to represent the task of dispatching media communicative acts to the relevant media design modules, and vice versa, to collect and pass on the results of the single design modules. While we assume that an IMMPS is capable of producing output in at least two different media, we do not assume an upper bound for the total number of design modules. Moreover, an IMMPS might even comprise several components for one medium but different modalities, for example, different graphics design components for different subtypes of graphics.
For the sake of generality, the RM does not provide fine grained
descriptions for the media/mode-specific design components.
We only note that media communicative acts constrain the employed
mechanism for designing media objects. Even for one and the same
medium or modality, different IMMPSs often include components which
rely on very different design mechanisms,
e.g., grammar-based, case-based, plan-based approaches, or
genetic programming approaches.
The Layout Design component (cf. Fig. 6) is responsible for the determination of the spatial/temporal arrangement of media objects in the presentation. The current RM does not further detail the layout task. We refer to the paper by Graf (see this issue) which outlines a reference model for Layout Systems. As indicated in Fig. 6 the Design Layer does not prescribe a particular ordering in which media design and layout design have to be carried out. No restriction has been made here since the following modes of operation may be supported by an IMMPS:
The results of the Design Layer are realization plans which are ordered sets of realization commands to be executed by dedicated realization components. We assume that media design and layout design have their counterparts at the following Realization Layer with the components Media Realization and Layout Realization. It should be clear that the former intends to handle media realization commands and the latter layout realization commands only; moreover, the exchange of information between the two layers is indicated by two separate arrows in Fig. 6 (and also in Fig. 8).