Sommerville-Software-Engineering-10ed

4.4 ■ Requirements specification 125
Register
patient
Export
statistics
Medical receptionist
View
personal info.
Manager
Generate
report
View record
Nurse
Edit record
Doctor
Figure 4.15 Use cases
for the Mentcare system
Setup
consultation
4.4.3 Use cases
Use cases are a way of describing interactions between users and a system using a
graphical model and structured text. They were first introduced in the Objectory
method (Jacobsen et al. 1993) and have now become a fundamental feature of the
Unified Modeling Language (UML). In their simplest form, a use case identifies the
actors involved in an interaction and names the type of interaction. You then add
additional information describing the interaction with the system. The additional
information may be a textual description or one or more graphical models such as
the UML sequence or state charts (see Chapter 5).
Use cases are documented using a high-level use case diagram. The set of use
cases represents all of the possible interactions that will be described in the system
requirements. Actors in the process, who may be human or other systems, are represented
as stick figures. Each class of interaction is represented as a named ellipse.
Lines link the actors with the interaction. Optionally, arrowheads may be added to
lines to show how the interaction is initiated. This is illustrated in Figure 4.15, which
shows some of the use cases for the Mentcare system.
Use cases identify the individual interactions between the system and its users or
other systems. Each use case should be documented with a textual description. These
can then be linked to other models in the UML that will develop the scenario in more
detail. For example, a brief description of the Setup Consultation use case from
Figure 4.15 might be:
Setup consultation allows two or more doctors, working in different offices, to
view the same patient record at the same time. One doctor initiates the consultation
by choosing the people involved from a dropdown menu of doctors who
are online. The patient record is then displayed on their screens, but only the
initiating doctor can edit the record. In addition, a text chat window is created