Table 9.1: Layering and associated degrees of existing architectures.
Table 9.2: Pseudo layers, partioned awareness, and different kinds of external modules.
Table 9.1 and 9.2 describe architectures of several existing collaboration systems. Table 9.1 gives the layering and associated degrees supported by them. Since all of these systems are collaboration tools, these values refer to the minimum values of these degrees, since some clients may create additional layers, replicas, processes, and threads in the application. We have assumed above that all view layers are build on top of widget layers so that a comparison of the various degrees is more meaningful. Table 9.2 indicates the other properties supported by them: pseudo-modules, partitioned awareness, and external modules to support session management, centralization, site-specific computing, collaboration awareness, and message servers. These tables show the similarities and differences among these tools. All systems except MMM support multi-workstation collaboration. Among these systems, Team Workstation is workstation-based; XTV, Shared X, and MMConf are window-based; and Rendezvous, Suite, Weasel, and DistView are view-based. MMM offers the pure centralized architecture; MMConf, GroupKit, and DistView the replicated architecture; and Team Workstation, XTV, Rendezvous, Weasel, and DistView the semi-replicated architecture. In all systems except Rendezvous, the distribution degree is the same as concurrency degree. From an architectural point of view, there are no differences between Suite and Weasel.