Part V: Software Engineering
and Implementation
Lecture Note 16
Unified Modeling Language (UML)
Class Diagram and Statechart Diagram
Systems Analysis and Design
Kendall & Kendall
Sixth Edition
CS206 System Analysis & Design
Note 16 By ChangYu
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Major Topics
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Class Diagram
Class Diagram Syntax
The steps for creating a Class Diagram
Statechart Diagram
Statechart Diagram Syntax
The steps for creating a Statechart
Diagram
CS206 System Analysis & Design
Note 16 By ChangYu
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Class Diagram
• Class Diagram is a static model which shows the
classes and the relationships among classes that
remain constant in the system over time.
• It is similar to Entity-Relationship Diagram (ER),
but the class diagram describes classes which
include attributes and operations.
• The class diagram is defined for one single use
case just like the sequence diagram was defined
for a single use case.
CS206 System Analysis & Design
Note 16 By ChangYu
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Example
An example illustrates a class diagram reflecting the classes and
relationships for the “Manage Appointment” use case.
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Syntax
A CLASS
• Represents a kind of person, place, or thing about
which the system will need to capture and store
information.
• Has a name typed in bold and centered in its top a
compartment.
• Has a list of attributes in its middle compartment.
• Has a list of operations in its bottom compartment.
• Does not explicitly show operations that are
available to all classes.
AN ATTRIBUTE
• Represents properties that describe the state of an
object.
• Can be derived from other attributes, shown by
placing a slash before the attribute’s name.
Class 1
-attribute 1
+operation1()
attribute name /
derived attribute name
AN OPERATION
• Represents the action or functions that a class can
perform.
• Can be classified as a constructor, query, or update
operation.
• Includes parentheses that may contain parameters or
information needed to perform the operation.
Operation name ()
An ASSOCIATION
• Represents a relationship between multiple classes, or
a class and itself.
• Is labeled using a verb phrase or a role name,
whichever better represents the relationship.
• Can exist between one or more classes.
• Contains multiplicity symbols, which represent the
minimum and maximum times a class instance can be
associated with the related class instance.
CS206 System Analysis & Design
Note 16 By ChangYu
1..*
0..1
verb phrase
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Class
• Class stores and manages information in the system.
• During analysis: classes can refer to the people, place,
events, and anything about the system.
• During design and implementation – specific artefacts,
such as windows, forms, and other objects used to
build the system.
• Each class has three compartment.
Class’s name (top),
Attributes (middle),
Methods (bottom)
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Attribute
• Attribute are properties of the class about which we
want to capture information.
– Example: Person class contains the attributes last name,
first name, address, phone, and birth date.
• At times, you may want to store derived attributes,
which are attributes that can be calculated or derived.
These special attributes are denoted by placing a slash
( / ) before the attribute’s name which can be derived
by subtracting the patient’s birthday from the current
date.
– Example: person class contains a derived attributes called
“/age”.
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• It is also possible to show the visibility (能見度) of
the attribute on the diagram. Visibility relates to
the level of information hiding to be enforced for
the attribute.
• The visibility of an attribute can be
– Public(+) : is one that is not hidden from any other
object. Other objects can modify its value.
– Protected (#) : is one that is hidden from all other
classes except its immediate (最接近的) subclasses.
– Private (-) : is one that is hidden from all other classes.
• The default visibility for an attribute is normally
private.
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Note 16 By ChangYu
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Operations
• Operations are functions that a class can perform.
• The functions are available to all classes are not
explicitly shown within the class rectangle.
– Example: create new instance, return a value for a particular
attribute, set a value for a particular attribute or delete a
instance.
• Operations that are unique to the class are included in
the class rectangle.
– Example: “generate cancellation fee”
in the Bill class. “cancel without notice”
in the Appointment class.
•
The three kinds of operation:
1. Constructor operation: to create a new instance of a
class.
–
–
Example, “insert()” in the patient class that creates a new
patient instance as patients are entered into the system.
This kind operations are not shown on class diagram, because
they are available to all the class.
2. Query operation: determines the state of an object
and makes information about the state available to the
system, but it will not alter the object.
–
Example, the calculate_last_visit() that determines when a
patient last visited the doctor’s office will result in the object’s
being accessed by the system, but it will not result in any
change to its information.
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3. An update operation will change the value of
some or all of the object’s attributes, which may
result in a change in the object’s state.
– Example: a change_status() operation changes
the status of a patient from new to current, or
schedule_appointment(appointment) operation
associates a patient with a particular
appointment.
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Note 16 By ChangYu
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Relationship
• A primary purpose of the class diagram is to show the
relationships or associations, that classes have with
one other.
• These are depicted on the class diagram by drawing
lines between class. Similar to the relationships on the
ER diagram.
• An association has a name, participating class and
multiplicity.
• When multiple classes share a relationship, a line is
drawn and labeled with either the name of the
relationship or the roles that the classes play in the
relationship.
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Example:
• The class Patient and the class Appointment are associated with
one another whenever a patient schedules an appointment.
• Thus a line labeled “schedules” connects patient and
appointment, representing exactly how the two classes are
related to each other.
• Also notice that there is a small solid triangle beside the name of
the relationship. The triangle allows a direction to be associated
with the name of the relationship.
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Note 16 By ChangYu
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A Class Shares a Relationship with Itself
Example:
• A patient’s being the primary insurance carrier for other
patients (e.g. their spouse, children)
• A line named primary insurance carrier was drawn between
the patient class and itself to depict the role that the class plays
in the relationship .
• A plus sign (+) is placed before the label to communicate that
it is a role as opposed to the name of the relationship.
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• Relationship also have multiplicity, which documents how an
instance of an object can be associated with other instances.
• Numbers are placed on the association path to denote the
minimum and maximum instances that can be related through the
association in the format:
Minimum number .. Maximum number
• The numbers specify the relationship from the class at the far end
of the relationship line to the end with the number.
Example, there is a “0..*” on the
appointment end of the “patient
schedule appointment” relationship.
This means that a patient can be
associated with zero through many
different appointments. At the patient
end of this same relationship there is a
“1”, meaning that an appointment must
be associated with one and only one
patient.
Examples of UML notations that indicate the nature of the
relationship between instances of one class and instances of another
class.
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An Association Class
– It has its own attributes and operations.
– It is shown as a rectangle attached by a dashed
line to the association path, and the
rectangle’s name matches the label of the
association.
– Example :
An illness (e.g. the flu) can be
Associated with many symptoms
(e.g. sore throat, fever) and a
symptoms can be associated
with many illnesses.
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Aggregation Association
• When classes actually comprise (包含) other classes.
• An aggregation expresses a part-of relationship
between a components object and an aggregate object.
• An aggregation is a stronger form of association
relationship . It is represented with a hollow diamond
at the aggregate end.
• An aggregation involves a set of distinct object
instances, one of which contains or is composed of the
others.
• Example:
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Aggregation
Examples:
Health Team
Doctor
Nurse
Administrative
Personnel
Doctors, nurses, and administrative personnel are “ a part of” a
health care team.
A car comprise the engine,
doors, and transmission.
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Generalization Association
• In generalizing a set of object classes into a more
general class, we abstract not only the common
attributes and relationship, but also the
common operations.
• A generalization path is shown as a solid line
from the subclass to the superclass, with a
hollow triangle at the end of, and pointing
toward, the superclass.
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Example:
• This figure tells us that
those employees and
patients are kinds of
persons.
• Nurses, doctors and
administrative staffs are
kinds of employee.
• Remember that the
generalization relationship
occurs when you need to
use words such as “is akind-of” to describe the
relationship.
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Creating a Class Diagram
Step 1: Identify Classes
– Identify what classes should be placing on the diagram.
– A class diagram shows the classes that are needed for
the system as a whole.
– Note: Creating a class diagram to represent the classes
and relationships only for the Customer Places Order
use case.
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Step 2: Draw Relationships between the classes.
– Example, the customer class is related to the other class
because a customer “places” an order.
• The customer can place zero or many orders
• An order can be associate with one and only one customer.
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Step 3: Examine the model for opportunities
to use aggregation or generalization
associations.
• E.g. CD Selections decided that marketing
material is best viewed as a collection of different
kinds of promotional materials (e.g. artist
information, sample clips and reviews), it may be
best to model marketing material as an
aggregation that includes other classes.
• E.g. CD Selections may want to leave room for
the opportunity to sell items other than CDs.
Therefore, the class diagram could include a class
called product that is a generalization of CD.
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In this figure shows the aggregation and generalization
associations.
Class Diagram for Customer Places Order
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Statechart Diagram
• A statechart diagram is a dynamic model that
shows the different states of the class and what
events cause the class to change from one state to
another.
• Typically not used for all classes, but just to help
simplify the design of algorithms for methods of
complex classes.
• E.g. a patient can change over time, from being
“new” to “current” or “former”.
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Note 16 By ChangYu
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Syntax
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This example illustrates a statechart diagram representing
the patient class in the context of a hospital environment.
– A patient enters a hospital and is admitted (許可) after
checking in.
– If a doctor finds the patient to be healthy, he or she will be
released and is no longer considered a patient after two weeks
have elapsed (時間過去).
– If a doctor finds the patient to be unhealthy, he or she remains
under observation until the diagnosis has been changed.
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State
• A state is a set of values that describe an object at a specific
point in time.
• It represents a point in an object’s life in which it satisfies some
condition, performs some action, or waits for something to
happen.
– Example (page29), states include entering, admitted, released
and under observation.
• A state symbol is a rectangle with rounded corners with a
descriptive label that communicates a particular state.
• An initial state symbol is a small solid filled circle.
• The attributes or properties of an object affecting the state that it
is in.
– Example (page 29), attributes that influence state transitions
are the patient’s hospital status and the diagnoses.
CS206 System Analysis & Design
Note 16 By ChangYu
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Event
• An event is something that takes place at a certain point
in time and changes a value(s) that describe an object,
which in turn changes the object’s state.
– Example (page 29), checking into the hospital, a healthy
diagnosis and a two-week time lapse are events that cause
changes to the patient’s state.
• Arrows connect the state symbols, representing the
transitions between states.
• Each arrow is labeled with the appropriate event name
and any parameters or conditions that may apply.
• A guard condition is a Boolean expression that
includes attribute values, which allows a transition only
of the condition is true.
– Example (page 29), the two transitions from admitted to
released and under observation contain guard conditions.
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Creating a Statechart Diagram
A statechart diagram is drawn to depict a single class from a class
diagram. When the classes are very dynamic and complex, it is
necessary to have a good understanding of their states over time
and the events that triggers the changes.
1. Set the context.
2. Identify the initial, final and stable states of the object.
3. Determine the order in which the object will pass
through the stable states.
4. Identify the events, actions and guard conditions
associated with the transitions.
5. Validate the statechart diagram.
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Note 16 By ChangYu
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Applying the concepts at CD Selections
Step 1: Determine the context of the statechart
diagram
– The context of a statechart diagram is
usually a class. However, it also could be
a set of classes, a subsystem, or an entire
system.
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Step 2: Identify the States
– Identify the various states that an order will have
over its lifetime.
– This information is gain from reading the use
case reports, talking with users, and relying on
the requirements-gathering techniques.
– Begin by writing the steps of what has happened
to an object over time, from start to finish.
– The following is an order from start to finish,
from the order’s perspective:
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1. The customer creates an order on the web.
2. The customer submits the order once he or she is finished.
3. The credit authorization needs to be approved for the order to
be accepted.
4. If denied, the order is returned to the customer for changes or
deletion.
5. If accepted, the order is placed.
6. The order is shipped to the customer.
7. The customer receives the order.
8. The order is closed.
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Step 3: Determine the sequence of the states that an
object will pass through during its lifetime.
– Using this sequence, we can place the states on to the
statechart diagram, in a left to right order.
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Step 4: Identify the events, actions, and guard conditions
associated with the transitions (轉變) between the states of
the object.
– Identify unique states that the order possesses and determine
exactly what causes each state to occur.
– Place state figures on the diagram to represent the states and
label the transitions to describe the events that are taking place
to cause the state changes.
– Example, the event “order is created” move the order from the
“initial” state to the “In process” state.
– During the “Processing” state, a credit authorization is
requested. The guard condition “Authorization =Approved”
prevents the order to move from the “Processing” state to the
“Placed” state unless the credit authorization has been
approved.
– Also, the guard condition “Authorization = Denied” prevents
the order to move from the “Processing” state to the “Denied”
(拒絕接受) state unless the credit authorization has been denied.
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Step 5: Validates the statechart by ensuring that each
state is reachable and that it is possible to leave all
states except for the finial states.
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