UML offers four diagrams to model the dynamic view of the application domain.
The interaction diagrams—sequence and collaboration—are used primarily to model the objects as they interact to satisfy the pathway of a given use-case.
Sequence diagrams have a longer history than collaboration diagrams and are typically preferred over collaboration diagrams. The two relay the same message, but in different formats. Of all of the UML dynamic diagrams, the sequence diagram is the most heavily used.
The state diagram models the lifecycle of one class. State diagrams appear most often in applications that have a real-time element (e.g., an embedded system). Often control and boundary classes might contain interesting state information ...