Information Technology Reference
In-Depth Information
Process Sale
Patient
Scheduler
Process Sale
Process Sale
Doctor
Process Sale
Clerk
Fig. 3.12
Use case diagram (Miller
2003
)
presented together, as it is here, the result is a use case diagram which describes
not how this medical clinic functions, but, rather, what it does.
Use case diagrams are helpful in determining the features of a system, as each
scenario can reveal some new information; in communicating with clients by
providing a non-technical visualization of what a system will do; and in testing, by
providing scenarios which can be used to develop test cases.
3.4.3 Sequence Diagram
As we have said, class and use case diagrams are considered static models of a
system. They describe the structure and function of a system. Sequence diagrams,
on the other hand, are a type of interaction diagram, which describe what takes
place when the various entities associated with a system interact. A sequence
diagram details not what operations are meant to do, but how they are performed,
which includes the following: what information is changed, what communication
takes place, and when those actions occur. Sequence diagrams, as the name sug-
gests, are sequential based and derive their structure from a timeline. The top of a
diagram represents the earliest time in the sequence, which then progresses
downward. The actions performed are known as communications and can be
thought of as the sending of messages. The objects involved in a message sequence
are listed from left to right according to the order in which they participate in that
communication. The diagram below is used to represent making a hotel reserva-
tion (Fig.
3.13
).
