For example, two modes of a simple valve might be open and closed. The way a device interacts with connected devices can depend on the current mode. Failures can be modeled as modes or as factors that precipitate or prevent transitions. Transitions between device modes can be determined by control variables, variable changes propagated through interdevice connections, or changes in system flows. The model structure can be recomposed during a simulation as the direction and activation of interconnections changes.
Activity models are also state-transition models.
The Integrate operator uses a discrete-time approach, providing periodic updates of variables based on a rate, which may be changed dynamically by external inputs. Complex behavior emerges from the interaction of devices that have simple models of internal continuous processes. This environment supports incremental model development, maintenance, and reuse. IMC-sequencer software monitored and controlled the model rather than the skills layer and hardware. The model included diverse components and systems for processing O 2 and CO 2 gases in a plant-growth chamber, crew chamber, and incinerator, and for storing gases and transferring them between chambers.