A new model for visual distributed computing is proposed by the present generation of high-end dataflow-based visualization systems such as AVS from AVS, Inc. (formerly Stardent Computer, Inc.), Explorer from SGI, or public domain packages such as apE from OSC or Khoros from UNM.
The computational model of AVS is based on a collection of parametric modules, that is, autonomous building blocks which can be connected to form processing networks. Each module has definite I/0 dataflow properties, specified in terms of a small collection of data structures such as field, colormap, or geometry. The Network Editor, operating as a part of the AVS kernel, offers interactive visual tools for selecting modules, specifying connectivity and designing convenient GUIs to control module parameters. A set of base modules for mapping, filtering, and rendering is built into the AVS kernel. The user extensibility model is defined at the C/Fortran level-new modules can be constructed and appended to the system in the form of independent UNIX processes, supported by appropriate dataflow interface.
From the MOVIE perspective, we see AVS-type systems as providing the interesting model for ``coarse grain'' modular extensibility of MovieScript, augmenting the native ``fine grain'' extensibility model discussed in Section 17.2.6. An AVS module interpolates between the concepts of a PostScript operator (since it ``consumes'' a set of input objects and ``produces'' a set of output objects) and a class instance (since it also contains GUI-based ``methods'' to control internal module parameters). This is illustrated in Section 17.6 where we compare various language models in the context of ``in large'' programming. Consequently, AVS-style modules can be used to extend both the functional and object-oriented layers of MovieScript towards the UNIX domain in the form of user-provided independent UNIX processes. Also, any third-party source or ``dusty deck'' software package can be converted to the appropriate modular format and appended to the MOVIE system in terms of similar interface libraries as developed for AVS modules. The advantage of the AVS extensibility model is maximal ``external'' software economy due to easy connectivity to third-party packages. The advantage of the MOVIE model, based on the MovieScript language extensibility, is maximal ``internal'' software economy within the native code volume, generated by MOVIE developers. The merging of both techniques is particularly natural in the MovieScript context since PostScript itself can be viewed as a dataflow language.
An independent near-term issue is designing MOVIE interfaces to current and competing packages such as AVS and Explorer. Various possible interface models can be constructed in which MOVIE server either plays the role of the compute server, offering high-level language tools for building AVS modules or it takes over the control and AVS is used as a high-quality rendering device.