UML Weekend Crash Course™ - To Parent Directory

54
Saturday Morning
In Use Case diagrams, people, systems, and devices are all referred to as actors. The icons
to model them may vary, but the concept remains the same. An actor is a role that an external
entity plays in relation to the system. To reiterate, an actor is a role, not necessarily a
particular person or a specific system. Figure 5-5 shows some actor icons.
Venue Manager
HR System
Satellite Feed
person example system example device example
Figure 5-5 Actor icons for the Use Case diagram
For example, an actor may be the role of a stock clerk placing products into inventory.
Later that day the same person might work receiving products from a delivery truck. The
same person played two roles. Likewise, many people can function in the same role. For
example, warehouses have many stock clerks.
Using roles helps keep you focused on how the system is being used rather than on the
current organization of the company into job titles and responsibilities. The things that
people do must be separated from their current job titles for the system to be able to cope
with the changes that are inevitable in any system.
How do you identify actors Listen to descriptions of the system. Listen for the roles
people perform when using the system. When multiple people perform the same function,
try to name the role they all share when performing the particular function.
Tip
Throughout the modeling effort, the vocabulary of the user will reveal most
of the key elements of the model. Watch for how parts of speech translate
into model elements; actors typically show up as the subject in sentences
describing how people use the systems.
Use Cases
Use Cases define the required features of the system. Without these features, the system
cannot be used successfully.
Each Use Case is named using a verb phrase that expresses a goal the system must
accomplish, for example, deposit money, withdraw money, and adjust account (see Figure
5-6). Although each Use Case implies a supporting process, the focus is on the goal, not
the process.