The common basis for the collaborators is the primary model, for instance, embodied by a simulation. Several derived models can depend on the primary model, and derived model could be related to a number of presentation models. When collaborating, the common basis should be the same for all the cooperators at every moment in time. To assure consistency, it is best to have the simulation act autonomously without the slightest interference. We will refer to this as non-interference. Non-interference does not restrict the possibility for each user to create his own perspective in any way. It does prevent somebody from rewinding, changing parameters or restarting the simulation while others do not want or expect this.
However, the need to stop, rewind or change parameters in a simulation is imminent. Considering multiple what-if situations, for example, is necessary when looking at different re-design alternatives, each with its own set of parameters. One way to meet this requirement, while upholding non-interference, is to store all past events in a database or to allow copies with different parameters of the simulation to be started.
While interaction with the primary model should be avoided as much as possible, derived models can be used in a more flexible manner. Several derived models can be created, all depending on one primary model. While the primary model can be considered a common basis that should not be interfered with, the derived model can be seen as a common workspace that permits interference. All participants of a session could use the same derived model or multiple derived models could be created, depending on the need to share information concepts or to be independent of the other users.