iming diagrams are one of the new artifacts added to UML 2. Timing diagrams are used to show changes and their relationship to clock times. It provides a visual representation of objects changing state and interacting over time. Timing diagrams can be used for defining hardware-driven or embedded software components.
There are two basic flavors of timing diagram, Timing diagrams can be drawn from a value or time based point of view. The X-axis of the timing diagram normally has the time units with the Y-axis showing the objects and their states. States are normally changed by some sort of event that causes the state change.
Example: Time-based timing diagram
Example: Value-based timing diagram