Chp 6 hw2

Chapter 6Object Modeling
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 Explain how object-oriented analysis can be
used to describe an information system
 Define object modeling terms and concepts,
including objects, attributes, methods,
messages, classes, and instances
 Explain relationships among objects and
the concept of inheritance
 Draw an object relationship diagram
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 Describe Unified Modeling Language (UML)
tools and techniques including use cases, use
case diagrams, class diagrams, sequence
diagrams, state transition diagrams, and
activity diagrams
 Explain the advantages of using CASE tools in
developing the object model
 Explain how to organize an object model
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 O-O methodology is popular because it
integrates easily with object-oriented
programming languages such as Java, Smalltalk,
VB.Net, Python, and Perl
 Programmers also like O-O code because it is
modular, reusable, and easy to maintain
 The end product of O-O analysis is an object
model
◦ Object model: Represents the information system in
terms of objects and O-O concepts
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 Object-Oriented Terms and Concepts
◦ Unified modeling language (UML)
 Method of visualizing and documenting an information
system
◦ Attributes: Characteristics that describe an object
◦ Methods: Tasks or functions that the object performs
◦ Message: Command to perform a specific function
◦ A class is a group of similar objects
 Instance: Specific member of a class
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 Objects
◦ Represented as a
rectangle
 The object name is at
the top, followed by
the object’s attributes
and methods
FIGURE 6-1 Objects have attributes,
can send and receive messages, and
perform actions called methods.
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FIGURE 6-2 The PARENT
object includes four
attributes and two
methods. Mary Smith,
Ahmed Ali, and Anthony
Greene are instances of
the PARENT object.
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FIGURE 6-3 The CHILD object includes five attributes and five methods. James Smith,
Amelia Ali, and Misty Greene are instances of the CHILD object.
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 Attributes
◦ Describe the characteristics of an object
◦ The number of attributes required depends on:
 Business requirements of the information system
 Requirements of users
◦ Attributes of an object are defined during the
system development process
◦ Objects possess a state
 State: Describes the object’s current status
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 Methods
◦ Specific tasks that an object can perform
◦ Identify functions performed
◦ Describe the functions performed
FIGURE 6-4 The MORE FRIES method
requires the server to perform seven
specific steps.
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 Message
◦ A command that tells an object to perform a certain
method
◦ Polymorphism: Concept that a message gives
different meanings to different objects
FIGURE 6-5 In an example of polymorphism, the message GOOD NIGHT
produces different results, depending on which object receives it.
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 Message (cont.)
◦ A message to the object triggers changes within the
object without specifying how the changes must be
carried out
 An object can be viewed as black box
◦ Encapsulation: Idea that all data and methods are
self-contained, as in a black box
Figure 6-6 In a school information system, an INSTRUCTOR object sends an ENTER GRADE
message to an instance of the STUDENT RECORD class.
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 Classes
◦ An object belongs to a group or category called a
class
 All objects within a class share common attributes and
methods
◦ Subclasses: Categories within a class
◦ Super-class: A class belonging to a general
category
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FIGURE 6-7 The VEHICLE class
includes common attributes and
methods. CAR, TRUCK, MINIVAN, and
SCHOOL BUS are instances of the
VEHICLE class.
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FIGURE 6-9 At the fitness center, the PERSON superclass includes common
attributes and methods. EMPLOYEE is a class within the PERSON superclass.
INSTRUCTOR is a subclass within the EMPLOYEE class.
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 Relationships
◦ Enable objects to communicate and interact as
they perform business functions and transactions
◦ Describe what objects need to know about each
other
 Inheritance
◦ The strongest relationship
◦ Enables an object to derive one or more of its
attributes from another object
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FIGURE 6-10 An inheritance relationship exists between the INSTRUCTOR and
EMPLOYEE objects. The INSTRUCTOR (child) object inherits characteristics
from the EMPLOYEE (parent) class and can have additional attributes of its own.
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 Object Relationship Diagram
◦ Displays objects and how they interact to perform
business functions and transactions
FIGURE 6-11 Object relationship
diagram for the fitness center.
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 UML uses a set of symbols to represent
graphically the various components and
relationships within a system
 Use Case Modeling
◦ Use case: Represents the steps in a specific
business function or process
◦ An external entity, called an actor, initiates a
use case by requesting the system to perform a
function or process
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 Use Case Modeling (Cont.)
◦ UML symbol for a use case is an oval with a label that
describes the action or event
◦ The actor is shown as a stick figure, with a label that
identifies the actor’s role
◦ Use case description: Documents the name of the use
case, the actor, a description of the use case
 Provides a step-by-step list of the tasks and other key
descriptions and assumptions
FIGURE 6-12 In a medical office system, a PATIENT
(actor) can MAKE APPOINTMENT (use case).
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FIGURE 6-13 When a student adds a class, PRODUCE FITNESS-CLASS ROSTER uses the results of
ADD CLASS to generate a new class roster. When an instructor changes his or her availability, UPDATE
INSTRUCTOR INFORMATION uses the CHANGE AVAILABILITY use case to update the instructor’s
information.
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FIGURE 6-14 The
ADD NEW
STUDENT use
case description
documents the
process used to
add a current
student into an
existing class.
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 Use Case Diagrams
◦ A visual summary of several related use cases
within a system or subsystem
◦ The first step is to identify the system boundary
which is represented by a rectangle
 System boundary: Shows what is included in the
system (inside the rectangle) and what is not included
in the system (outside the rectangle)
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FIGURE 6-16 A use case
diagram to handle work at
an auto service
department.
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 Class Diagrams
◦ Show the object classes and relationships involved
in a use case
◦ Each class appears as a rectangle, with the class
name at the top, followed by the class’s attributes
and methods
◦ Lines show relationships between classes and have
labels identifying the action that relates the two
classes
◦ Includes a concept called cardinality
 Cardinality: Describes how instances of one class
relate to instances of another class
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FIGURE 6-17 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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FIGURE 6-18 Class diagram
for a sales order use case
(attributes and methods
omitted for clarity).
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 Sequence Diagrams
◦ Dynamic model of a use case, showing the
interaction among classes during a specified time
period
◦ Graphically document the use case by showing the
classes, the messages, and the timing of the
messages
◦ Include symbols that represent classes, lifelines,
messages, and focuses
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 Sequence Diagrams (Cont.)
◦ Classes
 Send or receive messages
 Shown at the top of the sequence diagram
◦ Lifelines
 Represent the time during which the object above it is
able to interact with the other objects in the use case
 An X marks the end of the lifeline
◦ Messages
 Include additional information about the contents
◦ Focuses
 Indicate when an object sends or receives message
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FIGURE 6-19 A sequence diagram
with two classes. Notice the X that
indicates the end of the CLASS 2
lifeline. Also notice that each message
is represented by a line with a label
that describes the message, and that
each class has a focus that shows the
period when messages are sent or
received
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FIGURE 6-20 The sequence diagram for the ADD NEW STUDENT use case.
The use case description for ADD NEW STUDENT is shown in Figure 6 14.
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 State Transition Diagrams
◦ Show how an object changes from one state to
another, depending on events that affect the object
◦ All possible states must be documented in the state
transition diagram
◦ States appear as rounded rectangles with the state
names inside
FIGURE 6-21 An example of a
state transition diagram for a bank
account.
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 Activity Diagrams
◦ Show actions and events as they occur
◦ Show the order in which the actions take place and
identify the outcomes
FIGURE 6-22 An
activity diagram shows
the actions and events
involved in withdrawing
cash from an ATM.
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 Business Process Modeling (BPM)
◦ Represents the people, events, and interaction in a
system
◦ Can be used anytime during the systems
development process
◦ Compatible with object modeling
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FIGURE 6-23 The
Bizagi Modeler tool
supports business
modeling and simulation
using the standard BPM
notation.
Source: bizagi.com
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 CASE Tools
◦ Provide an overall framework for documenting the
system components
 Object modeling requires many types of diagrams to
represent proposed systems
 CASE tools speed up the process
◦ Ensure consistency and provide common links
 Once objects are described and used in one part of the
design, they can be reused multiple times without
further effort
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 Develop an object relationship diagram that
provides an overview of the system
 Support each diagram or object definition
with clear and relevant documentation that
can be accessed easily
◦ Organize use cases and use case diagrams so they
can be linked to the appropriate class, state
transition, sequence, and activity diagrams
 Maintain accuracy
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Object modeling is a popular technique that
describes a system in terms of objects
• Object-oriented terms include classes,
attributes, instances, messages, and
methods
 Objects can send messages, or commands,
that require other objects to perform certain
methods, or tasks
•
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 The Unified Modeling Language (UML) is a
widely used method of visualizing and
documenting an information system
 Use case describes a business situation
initiated by an actor, who interacts with the
information system
 At the end of the object modeling process,
the use cases and use case diagrams are
organized and class, sequence, state
transition, and activity diagrams are created
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