State diagrams can also help us develop the requirements and consider software and hardware requirements that may not be so easily evoked from the customer.  The state diagram describes the behavior or the software / system, specifically the number of states in which the product may be.  There will be transitions between states defined by certain actions. For example, an instrument cluster may go into a “sleep mode” when the key is outside of the ignition.  Inserting the key and moving it forward to start the vehicle; will transition the instrument cluster from sleep mode and the features that may be available, to “on” mode where different set if features and performance expectations will reside.  For example, in sleep mode, we may press a button to see the odometer or clock in the instrument cluster.  Moving to key forward we may see pointers move and the instrument cluster to perform a lamp check. That is, do all of the lights and tell tales illuminate.

Each of these states may have a set of features or functions associated. Additionally, we understand how the product will need to respond.  We will gain an understanding of the hardware needs and the software structure through this view of the product.

State Diagram Example