Object Modeling OBJECT-ORIENTED ANALYSIS AND MODELING USING THE UML Read: Chapter 6

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Object ModelingOBJECT-ORIENTED ANALYSIS AND
MODELING USING THE UML Read Chapter 6

• Dr Manolya Kavakli
• Department of Computing
• Macquarie University
• Sydney, Australia

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Chapter Objectives

• 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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Chapter Objectives

• 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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Introduction

• You learn about object-oriented analysis, which
  is another way to view and model system
  requirements
• You use object-oriented methods to document,
  analyze, and model the information system

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Introduction to Object Modeling

• Object-oriented analysis (OOA)
• an approach used to
• study existing objects to see if they can be
  reused or adapted for new uses
• define new or modified objects that will be
  combined with existing objects into a useful
  business computing application
• Object modeling a technique for identifying
  objects within the systems environment and the
  relationships between those objects.

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Overview of Object-Oriented Analysis

• Object-oriented analysis is a popular approach
• sees a system from the viewpoint of the objects
  themselves as they function and interact

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Overview of Object-Oriented Analysis

• Object-Oriented Terms and Concepts
• Unified Modeling Language (UML)
• Attributes
• Methods
• Message
• Class
• Instance

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Objects, Attributes, Instances

• Object something that is or is capable of
  being seen, touched, or otherwise sensed, and
  about which users store data and associate
  behavior.
• Person, place, thing, or event
• Employee, customer, instructor, student
• Warehouse, office, building, room
• Product, vehicle, computer, videotape
• Attribute the data that represent
  characteristics of interest about an object.
• Object instance each specific person, place,
  thing, or event, as well as the values for the
  attributes of that object.

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Objects, Attributes, Instances (cont.)
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Overview of Object-Oriented Analysis

• Objects

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Overview of Object-Oriented Analysis

• Objects

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Overview of Object-Oriented Analysis

• Objects

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Overview of Object-Oriented Analysis

• Objects

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Overview of Object-Oriented Analysis

• Attributes
• If objects are similar to nouns, attributes are
  similar to adjectives that describe the
  characteristics of an object
• Some objects might have a few attributes others
  might have dozens
• State
• Describes the objects current status

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Overview of Object-Oriented Analysis

• Methods
• A method defines specific tasks that an object
  can perform
• Just as objects are similar to nouns and
  attributes are similar to adjectives, methods
  resemble verbs that describe what and how an
  object does something

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Method (Behavior) Encapsulation

• Behavior the set of things that the object can
  do that correspond to functions that act on the
  objects data (or attributes).
• In object-oriented circles, an objects behavior
  is commonly referred to as a method, operation,
  or service.
• For object order
• Addorder
• Deleteorder
• modifyorder

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Overview of Object-Oriented Analysis

• Polymorphism
• The same message to two different objects can
  producethe same result.
• Black box
• A messages triggers changes within the object
  without specifying how the changes must be
  carried out.
• E.g., Gas pump
• Blackbox is an example of Encapsulation
• All data and methods are self-contained.
• The object prevents its internal code from being
  altered by another object.

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Overview of Object-Oriented Analysis

• Messages
• A major advantage of O-O designs is that systems
  analysts can save time and avoid errors by using
  modular objects, and programmers can translate
  the designs into code, working with reusable
  program modules that have been tested and
  verified
• These objects could be used by other schools

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Overview of Object-Oriented Analysis

• Classes
• An object belongs to a group or category called a
  class
• All objects within a class share common
  attributes and methods
• Subclasses
• Superclass

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Overview of Object-Oriented Analysis

• Classes

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Relationships Among Objects and Classes

• Inheritance
• enables a child object to derive attributes from
  a parent object.
• Child
• Parent

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Relationships Among Objects and Classes

• Object Relationship Diagram
• provides an overview of the system.

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UML

• Unified Modeling Language (UML) a set of
  modeling conventions that is used to specify or
  describe a software system in terms of objects.
• The UML does not prescribe a method for
  developing systems
• only a notation that is now widely accepted as a
  standard for object modeling.
• DFDs model data and processes
• UML describes OO systems

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Object/Class Relationships

• Object/class relationship a natural business
  association that exists between one or more
  objects and classes.

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Aggregation

• Aggregation a relationship in which one larger
  whole class contains one or more smaller
  parts classes. Conversely, a smaller part
  class is part of a whole larger class.

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Composition

• Composition an aggregation relationship in
  which the whole is responsible for the creation
  and destruction of its parts. If the whole
  were to die, the part would die with it.

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Messages

• Message communication that occurs when one
  object invokes another objects method (behavior)
  to request information or some action

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Object Modeling with the Unified Modeling Language

• The UML uses a set of symbols to represent
  graphically the various components and
  relationships within a system
• It mainly is used to support object-oriented
  systems analysis and to develop object models

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Object Modeling with the Unified Modeling Language

• Use Case Modeling
• Actor
• Symbol for a use case is an oval with a label
  that describes the action or event
• Use cases also can interact with other use cases

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Object Modeling with the Unified Modeling Language

• Use Case Modeling
• When the outcome of one use case is incorporated
  by another use case, we say that the second case
  uses the first case
• Use case description
• When you identify use cases, try to group all the
  related transactions into a single use case

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Object Modeling with the Unified Modeling Language

• Use Case Diagrams
• Use case diagram
• System boundary
• After you identify the system boundary, you place
  the use cases on the diagram, add the actors, and
  show the relationships

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Object Modeling with the Unified Modeling Language

• Class Diagrams
• Class Diagram
• Evolves into a physical model and finally becomes
  a functioning information system
• Each class appears as a rectangle, with the class
  name at the top, followed by the classs
  attributes and methods
• Cardinality

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Object Modeling with the UML

• Class Diagrams represents a detailed view of a
  single use case
• Show classes and their relationships

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Object Modeling with UML

• Sequence Diagrams dynamic model of a use case,
  showing the interaction over time
• Sequence diagram
• Include symbols such as
• Classes
• Lifelines duration of interaction
• X end of lifeline
• Messages
• Focuses indicate when an object sends/receives
  messages

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Object Modeling with the Unified Modeling Language

• State Transition Diagrams show how an object
  changes from one stateto another, depending on
  events

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Object Modeling with the Unified Modeling Language

• State Transition Diagrams
• The small circle to the left is the initial
  state, or the point where the object first
  interacts with the system
• Reading from left to right, the lines show
  direction and describe the action or event that
  causes a transition from one state to another
• The circle at the right with a hollow border is
  the final state

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Object Modeling with the Unified Modeling Language

• Activity Diagrams resembles a horizontal
  flowchart that shows the actions and events as
  they occur

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Object Modeling with the Unified Modeling Language

• Activity Diagrams
• Sequence diagrams, state transition diagrams, and
  activity diagrams are dynamic modeling tools that
  can help a systems analyst understand how objects
  behave and interact with the system

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Object Modeling with the Unified Modeling Language

• CASE Tools
• Object modeling requires many types of diagrams
  to represent the proposed system
• Creating the diagrams by hand is time-consuming
  and tedious, so systems analysts rely on CASE
  tools to speed up the process and provide an
  overall framework for documenting the system
  components

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• UML http//www.youtube.com/watch?v2yoahl1Hf5Ufea
  turerelated
• MicroSoft Visio
• http//www.youtube.com/watch?vgCMWCBLl7Q4feature
  related
• http//www.youtube.com/watch?vxmDjmm0btO8feature
  related

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Organizing the Object Model

• You should develop an object relationship diagram
  that provides an overview of the system
• You should organize your use cases and use case
  diagrams so they can be linked to the appropriate
  class, state transition, sequence, and activity
  diagrams
• It is much easier to repair a diagram now than to
  change the software later

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Modeling the Functions of the System

• The following steps evolve the requirements
  use-case model into an analysis use-case model
• Identify, define, and document new actors.
• Identify, define, and document new use cases.
• Identify any reuse possibilities.
• Refine the use-case model diagram (if necessary).
• Document system analysis use-case narratives.
• System analysis use case a use case that
  documents the interaction between the system user
  and the system. It is highly detailed in
  describing what is required but is free of most
  implementation details and constraints.

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Revised System Use-Case Model Diagram
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Use-Case Narrative
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Use-Case Narrative (cont.)
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Abstract Use-Case Narrative
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Modeling Use-Case Activities

• Activity diagram a diagram that can be used to
  graphically depict the flow of a business
  process, the steps of a use case, or the logic of
  an object behavior (method).
• One or more activity diagram can be constructed
  for each use case (more than one if use case is
  long or contains complex logic).
• Solid dot represents the start of the process.
• A rounded-corner rectangle represents an
  activity or task that needs to be performed.
• Arrows depict triggers that initiate activities.
• A solid black bar is a synchronization bar that
  allows you to depict activities that occur in
  parallel.

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Example of an Activity Diagram
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Finding and Identifying the Business Objects

• Find the Potential Objects
• Review each use case to find nouns that
  correspond to business entities or events.
• Select the Proposed Objects
• Not all nouns represent business objects.
• Ask
• Is the candidate a synonym of another object?
• Is the candidate outside the scope of the system?
• Is the candidate a role without unique behavior,
  or is it an external role?
• Is the candidate unclear or in need of focus?
• Is the candidate an action or an attribute that
  describes another object?

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Partial Use-Case Narrative with Nouns Highlighted
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Potential Object List
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Proposed Object List
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Organizing the Objects and Identifying their
Relationships

• Identifying Associations and Multiplicity
• Identifying Generalization/Specialization
  Relationships
• Identifying Aggregation Relationships
• Prepare the Class Diagram
• Class diagram a graphical depiction of a
  systems static object structure, showing object
  classes that the system is composed of as well as
  the relationships between those object classes.

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Chapter Summary

• This chapter introduces object modeling, which is
  a popular technique that describes a system in
  terms of objects
• The Unified Modeling Language (UML) is a widely
  used method of visualizing and documenting an
  information system
• At the end of the object modeling process, you
  organize your use cases and use case diagrams and
  create class, sequence, state transition, and
  activity diagrams