o
Reviewthe
behavioralmodel to verify accuracy and consistency.
Identifying Events with the
Use Case
·
The
use case represents a sequence of activities that involves actors and the
system.
·
In
general, an event occurs whenever the system and an actor exchange information.
·
It
has been indicated that an event is not the information that has been
exchanged, but rather the fact that information has been exchanged.
·
For
example : The use case for a portion of the SafeHome security function.
·
The
homeowner uses the keypad to key in a four-digit password. The password is
compared with the valid password stored in the system. If the password is
incorrect, the control panel will beep once and reset itself for additional
input. If the password is correct, the control panel awaits further act.
·
The
underlined portions of the use case scenario indicate events. An actor should
be identified for each event; the information that is exchanged should be
noted,.
·
Here
the object, Homeowner, transmits an event to the object ControlPanel. The event
might be called password entered.
State Representations
·
In
the context of behavioral modeling, two different characterizations of states
must be considered:
o
The
state of each class as the system performs its function and
o
The
state of the system as observed from the outside as the system performs its
function.
·
The
state of a class takes on both passive and active characteristics.
o
A
passive state is simply the current status of all of an object’s attributes.
o
The
active state of an object indicates the current status of the object as it
undergoes a continuing processing.
·
For
example, the passive state of the class Player (in the video game application)
would include the current position and orientation attributes of Player as well
as other features of Player that are relevant to the game .
·
The
class Player might have the following active states:
o Moving, at rest, injured, being
cured;, lost etc.
·
An
event (sometimes called a trigger) must occur to force an object to make a
transition from one active state to another.
State diagram
·
One
component of a behavioral model is a UML state diagram that represents active
states for each class and the events (triggers) that cause changes between
these active states.
·
Figure (In
Previous Slide) illustrates
a state diagram
for the ControlPanel object in
the Safe Home security function.
·
Each
arrow shown in Figure represents a transition from one active state of an
object to another. The labels shown for each arrow represent the event that
triggers the transition.
·
An
action occurs concurrently with the state transition, generally involves one or
more operations (responsibilities) of the object.
·
For
example, the action connected to the password entered event (ing Figure) is an
operation named validatePassword() that accesses a password object and performs
a digit-by-digit comparison to validate the entered password.
The States of a System
·
state—a
set of observable circum-stances that characterizes the behavior of a system at
a given time.
·
state
transition—the movement from one state to another.
·
event—an
occurrence that causes the system to exhibit some predictable form of behavior.
·
action—process
that occurs as a consequence of making a transition.
·
state—a
set of observable circum-stances that characterizes the behavior of a system at
a given time.
·
state
transition—the movement from one state to another.
Sequence diagram
·
The
second type of behavioral representation, called a sequence diagram in UML,
indicates how events cause transitions from object to object.
·
Once
events have been identified by examining a use case, the modeler creates a
sequence diagram.
o
It
is a representation of how events cause flow from one object to another as a
function of time.
o
The
sequence diagram is a shorthand version of the use case. It represents key
classes and the events that cause behavior to flow from class to class.
·
For
example: Figure (In Next Slide) illustrates a partial sequence diagram for the
SafeHome security function.
o
Each
of the arrows represents an event (derived from a use case)
o
It
indicates how the event channels behavior between SafeHome objects.
o
Time
is measured vertically (downward),
o
Narrow
vertical rectangles represent time spent in processing an activity.
Sequence diagram
·
Explanation
of Figure: The first event, system ready, is derived from the external
environment and channels behavior to the Homeowner object.
·
The
homeowner enters a password. A request
lookup event is passed to System, which looks up the password in a simple
database and returns a result (found or not found) to ControlPanel (now in the
comparing state).
A valid password results in
a password=correct event to System,
which activates Sensors with a request activation event. Ultimately, control is
passed back to the homeowner with the activation successful event.
Points to remember when creating these
diagrams
State
diagram
·
It
shows the object undergoing a process.
·
It
gives a clear picture of the changes in the object's state in this process.
·
For
example ATM withdraw Card
·
object
state: Checking, Approving, Rejecting.
·
Sequence diagrams is that,it is
a good at showing
|
|
sequential logic but
not that
|
|
good at giving you a "big
picture
|
|
view “.
|
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![Modularity [Divide complex problem in small parts]](https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhz_eGw88xz6gpPRk-gVgKW_YRhGoLQcO0iMXCgMk86kbhF5tVaD-rkKltVeUJlVo72b8C_R9332hmymv_rZ94_rooed61TyHa2YpbSh4wAl0hU-p1VXmdyx-C2lE4Jn8wdCHqf8q_LmnWy/s1600/modularityExample.jpg "Modularity [Divide complex problem in small parts]")
