Download as a PDF

Figure 3. Sequence Diagram: Registration – Confirmation Process.
Figure 3 is a sequence diagram showing an alternative
explanation of the Registration and Confirmation processes.
We have found that some students prefer to work with the
material as an activity diagram, while others prefer the
equivalent sequence diagram.
The vertical lines in the sequence diagram are called lifelines
and represent the object’s life during the interaction. This
representation is particularly useful to the object-oriented
developer as a way of depicting the overall flow of control
that takes place in a typical interaction. Inter-object messages
are represented by solid arrows between the involved
lifelines; messages are invocations to the methods supplied
by each object. Information returned by the invoked methods
is denoted by broken lines. The order in which those
messages are sent is shown from top to bottom of the
diagram. Messages have at least a unique name and a list of
optional parameters. Special messages – called self
delegation – represent recursive communication in which the
object calls itself and are denoted by arrows back to the same
lifeline.