First and most importantly, I will define what a use case
is. A use case is a tactic used in system analysis to identify, clarify, and categorize
system requirements. The use case is made up of a set of possible sequences of
interactions between systems and users within an environment and related to a
particular goal. The use case should contain all system activities that have
significance to the users within a given system.
What Use Cases Do
They hold Functional Requirements in an easy to read and tracking
They represent the goal of an interaction between an actor and the
They are multi-level, one use case can use/extent the functionality of
What Use Cases Do Not Do
They don't specify user interface design. They specify the intent, not
the action Detail.
They don't specify implementation detail.
Actor: An actor is something with behavior, such as a person, computer
system, or organization.
Scenario: A scenario is a specific sequence of actions and interactions
between actors and the system under discussion; it is also called a use case
instance. It is one particular story of using a system, or one path through the
use case; for example, the scenario of successfully using an ATM machine to
Now that I have introduced what a use case is, what they do,
what they do not do, and provided the definition of an actor and scenario, let
us look at a complete UML diagram of the ATM cash withdrawal transaction. While
this diagram is not all inclusive to actions involved with using an ATM, it
should provide the foundation as to how to create a use case diagram and how to
interpret its meaning.
Figure 1: Example UML ATM System Usage Use Case
Now that I have covered the definition of a use case, what
they do, what they do not do, and provided a sample diagram, we will move into
the various sections contained within a use case.