Sequence diagram

This diagram depicts the processes and objects involved and the sequence of messages exchanged as needed to carry out the functionality.

Sequence diagrams are typically associated with use case realizations in the 4+1 architectural view model of the system under development.

There are two kinds of sequence diagrams: A sequence diagram shows, as parallel vertical lines (lifelines), different processes or objects that live simultaneously, and, as horizontal arrows, the messages exchanged between them in the order in which they occur.

Familiarity with unified modeling language (UML) is needed to construct a system sequence diagram.

Messages will often appear at the top or bottom of a system sequence diagram to illustrate the action in detail.

If a caller sends an asynchronous message, it can continue processing and need not wait for a response.

Objects calling methods on themselves use messages and add new activation boxes on top of any others to indicate a further level of processing.