Machines can take on many forms, including this one which is flat and would be formally described by a network of activity nodes and arcs among them. The above example is a machine (or automaton) that is defined by flow, as are all automata. The automaton models the censorship process in Iran beginning with the Supreme Leader and then cascading down to the enforcers. This machine is constructed by The Annenberg School for Communication at the University of Pennsylvania. There is a complete description of the process, with the above figure at its original resolution at their web site. Nodes are points of control and arcs probably carry both control and data flow. Curiously, there is very little feedback in this architecture (only at the very end). There is also an interesting correlation between the abstract semantics of machines and Iran's censorship process: power flows from top to bottom (both literally and figuratively). Machines of this sort are a bit different than those in some of the other posts because they are often called models--specifically simulation models. To be more precise, this is a simulation model of the censorship process.