In the
Unified Modeling Language (UML), use case diagram is a set of scenarios
that
describing and interaction between a user and a system. Use cases are
used during
the
analysis phase of a project to identify and partition system
functionality.
The Use
Case diagram is used to identify the primary elements and processes that
form the
system. The primary elements are termed as "actors" and the processes
are
called
"use cases". It captures the functional aspects of a system. It displays
the
relationship among actors and use cases. It describes a sequence of
actions
that
provide something of measurable value to an actor and is drawn as a
horizontal
ellipse.
This
type of diagrams are used in almost every project, because they are
helpful
in
exposing requirements and planning the project. In the drawing of use
case diagram,
connect
the actors with the use cases with which they are involved, if an actor
supplies
information, initiates the use case, or receives any information as a
result
of the
use case, then there should be an association between them.
There are two main components of a use case diagram:Actor
An actor
is a person, organization, or external system that plays a role in one
or more
interactions with the system. It interact with use case, for example,
for
modeling
a banking application, a customer entity represents an actor in the
application.To
identify
an actor, search in the problem statement for business terms that
portray
roles in
the system. An actor is shown as a stick figure in a use case diagram
depicted
as shown
Use Case
Use
cases describe the behavior of the system when the actors sends one
particular
stimulus. A use case is shown as an ellipse in a use case diagram as
shown:
Associations
Associations between actors and use cases are indicated in use case diagrams by solid lines. It exists whenever an actor is involved with an interaction described by a use case. They are modeled as lines connecting use cases and actors to one another, with an optional arrowhead on one end of the line, that is often used to indicating the direction of the initial invocation of the relationship or to indicate the primary actor within the use case.
System boundary
A
rectangle is drawn around the use cases, called the system boundary box,
that
indicates the scope of system. Anything within the box represents
functionality
that is
in scope and anything outside the box is not. A system can not have
infinite
functionality, the system boundary defines the limits of the system. It
shows as:
Example of Use Case Diagram
This
diagram can easily be expanded until a complete description of the
ordering
system
is derived capturing all of the requirements that the system will need
to
perform.
Use cases are powerful tools for analysts to use when partitioning the
functionality of a system.
Use case
relationships and the corresponding diagrams help analysts to structure
use
cases such that their textual descriptions contain a minimum of
redundant information;
thus
making the whole text document much easier to maintain. But use cases
are not
design
tools. They do not specify the structure of the eventual software, nor
do
they
imply the existence of any classes or objects. They are purely
functional descriptions
written
in a formalism that is completely separate from software design.