State transition diagrams support the modeling of real-time systems, in which simultaneous processing of inputs is required.

The life cycle of an engineering solution to a problem ranges from problem-dominated (finding the optimum solutions for the user requirements) to implementation-dominated (pushing the technical feasibility and limitations). Therefore, there must be a clear way to distinguish between the formulation of the problem and the technology that is chosen to implement the problem.

A real-time system is typically connected to sensors such as thermocouples, optical scanners, and contact probes, and can thus collect a continuous stream of unstructured data, analogous to the senses of living organisms. These inputs are used to continually change outputs, in a feedback system much like an “eye-hand coordination.” Such a system can also produce physical changes in the environment it exists in, such as temperature changes, valve positions, and so on.

Real-time systems usually require the simultaneous processing of multiple inputs to correlate values. The speed and precision demanded of real-time systems is faster and more critical than that of other systems.

State Transition diagrams consist of states and transitions (to other states). A transition consists of both a condition and an action. Every incoming data flow into a process in the DFD must be associated with an appropriate condition on the corresponding state-transition diagram. Every outgoing data flow from a process must correspond to an appropriate action on the state-transition diagram.

The following commands are available on the Draw menu for the state transition diagram: