Object Orientation

1
Object Orientation

• An alternative approach to systems development
• No longer a fad
• Includes concepts, tools, methodologies and
  languages
• Represents a fundamentally different way of
  looking at systems and breaking them down into
  parts

2
What is an object?

• An object has both data and operations
• An objects data is the information about the
  object
• An objects operations represent things that
  happen that affect the objects data
• This is called encapsulation
• An object represents a major element of the
  system
• Merges the process-driven and data-driven
  perspectives

3
Example Banking

• Object Customer
• data
• Name Joe Smith
• Address 434 Maple St., Metro City, MD 92388
• operations
• new_customer
• change_address
• delete_customer

• Object Account
• data
• AccountNumber 2543238
• DateOpened 12/15/1998
• CurrentBalance 123.52
• AccountType checking
• operations
• new_account
• make_deposit
• make_withdrawal
• close_account

4
Instantiation

• Class a collection of objects, all of which
  have the same set of attributes (different
  values) and operations
• The objects that belong to a class are called
  instances of that class
• The class is instantiated when an object of that
  class is created
• Example Joe Smith is an instance of Customer

5
Specialization and Generalization

• Classes can form a hierarchy, where more general
  classes are specialized into more specific
  classes
• Example The class Student can be specialized
  into the classes Undergraduate Student and
  Graduate Student
• Example The classes Frozen Food, Canned Food,
  and Perishable Food can be generalized into the
  class Food Item

6
Specialization and Generalization
Food Item
Student
Frozen Food
Perishable Food
Undergraduate Student
Graduate Student
Canned Food
7
Inheritance

• A child class inherits all its parents
  attributes and operations
• A child class can also have other attributes and
  operations that did not come from the parent
• A child class can override an inherited operation
  with another operation with the same name - one
  form of polymorphism

8
OO Tools for Analysis Design

• Use cases - scenarios that describe users
  requirements from the users point of view
• Class diagram - defines the class hierarchy
• State diagram - defines the events that affect
  objects
• Sequence diagram - the logical design of a use
  case

9
Use Cases

• Each use case represents a complete scenario
  describing how the system is used by some actor
• An actor represents a role that a user plays one
  user can play several roles
• Use case scenarios are initiated by the actor,
  and can involve more than one actor
• There can be relationships between use cases

10
Use Case Diagram
Rent video
Return video
Video Store Clerk
Video Store Customer
ltlt extends gtgt
Calculate late fees
11
Class Diagrams

• Similar to ER diagrams, except operations are
  added
• Classes are like entities
• Attributes are the same concept
• Associations are like relationships
• Operations are new
• Shows the hierarchy of classes and their
  specializations and generalizations

12
Class Diagram Examples
Account
Customer
Account DateOpened CurrentBalance AccountType ne
w_account make_deposit make_withdrawal close_accou
nt
Owns
Name Address new_customer change_address delete_c
ustomer
1..
0..
owner
13
Class Diagram Examples
14
Class Diagram Examples
Flash
1..
1..
1..
0..
fits
uses
Test(Camera)
0..
requires
requires
Battery
size type
0..1
0..1
15
State Diagrams

• A state of an object is some condition that it
  satisfies most objects have many possible
  states, but they are in only one state at a time
• An event is something that occurs at a specified
  point in time that changes an objects state
• A state transition is when an object changes from
  one state to another as a result of an event

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State Diagram Example
Customer
Makes purchase / LastPurchaseDate CurrentDate
Makes inquiry
Prospective
6 months
Makes purchase / LastPurchaseDate CurrentDate
Current
CurrentDate - LastPurchaseDate gt 1 year
Former
3 years
Makes purchase / LastPurchaseDate CurrentDate
17
Rapid Application Development

• Motivated by the need for shorter development
  cycles
• A general strategy for developing systems faster,
  not a specific methodology or technique
• Appropriate when the number one concern is to
  produce a system quickly

18
Basic RAD Concepts

• Streamlining the SDLC process
• combining phases
• eliminating iteration
• User involvement
• helps ensure quick acceptance at end
• helps eliminate iteration
• Integrated CASE tools
• rapid prototyping
• minimizing effort to transform prototype to
  working system

19
Tools used in RAD

• Prototyping
• quickly design and generate parts of interface
• Code generation
• eliminates need for handwriting source code
• generates software from a design
• Visual development environments
• facilitates coding, especially implementing GUI
  interfaces
• JAD

20
RAD Advantages

• Products developed more quickly
• End product is more closely aligned with user
  needs because of less time between requirements
  and delivery
• Often lower costs
• System more aligned with user needs
• Makes it possible to produce systems in rapidly
  changing environments

21
RAD Disadvantages

• Quality often suffers
• interface consistency lacking
• no adherence to standards
• reusability and maintainability
• No time for in-depth understanding of the
  organizational environment
• risk of a major mismatch that is not understood
  until the end of the process
• High dependence on users willingness to be
  involved throughout the process