CS 3050

1
CS 3050

• Development using the Object Oriented Approach

2
Objectives

• The Benefits of OO Development
• Productivity
• Maintainability
• Extendibility
• Problems with OO Approach
• Changing to the OO Approach
• Preparing for Your Own Change to OO Development

3
Introduction

• The OO approach is a different way of developing
  systems.
• Some analysts claim that the OO approach implies
  a paradigm shift, a different way of viewing the
  world.
• Some problems from the shift result from the
  transition from traditional system development.
• This transition can be a major undertaking, one
  that requires a great commitment of resources.

4
The Benefits of OO Development

• The increase in productivity has not kept pace
  with the increase in demand for speedy delivery
  of new software.
• Existing software needs massive maintenance
  effort to keep them operational.
• Some companies spend up to 80 resource for
  maintenance.

5
Maintenance Requirement

• There are 4 reasons for the maintenance
  requirement
• Specifying and programming software systems a
  complicated undertaking -logical and syntactical
  code errors usually occur.
• Requirements specification - a major challenge in
  systems development. Do not always reflect users
  real needs which is often not even clear to users
  until after the first version of the software is
  running.
• Additional features that could not be
  accommodated in the original development might be
  needed.
• The business environment that the software is
  supporting might be changing.

6
Productivity

• From a programming perspective, there are many
  problems that a traditional functional language
  does not lend itself to solving easily.
• In most cases the use of OO language tends to
  result in shorter and more compact program code.
• OO allows a building block approach to system
  development. Assembling application using
  existing classes and libraries resulting in
  significant increase in productivity.

7
Reuse

• Can modules generated from structured programming
  be reused?
• Why is reuse in the design of Object-Oriented
  systems highlighted?
• goto ReuseResponse.rtf

8
Maintainability and Quality

• Improved maintenance is main advantage of a OO
  system.
• OO software is constructed using self-contained
  object classes. Object tend to be small in terms
  of number of programming statements that are
  needed to implement them creating manageable
  units within the system.
• Less complexity, fewer errors and reduced code.

9
Missing or Incorrect Specifications

• Specifications define what to build. Problems
  often because wrong specifications and poor
  understanding of the user needs.
• Traditional information systems were developed
  using structured development approach and common
  modeling techniques like data flow diagramming
  and data modeling.
• Unlike the traditional approach, OO approach
  promises to narrow down the communication gap by
  using modeling concepts and techniques that are
  more closely related to the users way of
  thinking.
• Object models allow us to remain in the same
  modeling context for the duration of the project,
  thereby also increasing the quality of the
  development effort.

10
Extendibility

• A system will eventually need to be changed
  either because all required functionality was not
  included or business needs changed.
• Adding features With OO approach, method and
  attributes can be added to existing object
  classes without disrupting the rest of the
  system. Using the inheritance feature new classes
  can be easily added.
• New features can be added using an incremental
  approach. The main functionality can be made
  available quickly for users and additional
  features can be added when time allows.

11
Problems with the OO Approach

• The potential benefits are not easily attainable.
  Using OO technology it is still possible to
  design a truly awful system in terms of quality
  and maintainability.
• OO technologies and development methods are still
  not mature or stable. Any large-scale change to
  new technology and methods is likely to be time
  consuming. Also there is a substantial learning
  curve. Productivity and quality decreases as
  staff is learning new methodology.
• Some benefits will show up only after a
  considerable amount of time. Benefits from reuse
  are only achievable after a certain portfolio of
  system has been developed.

12
Changing to OO Approach

• There are three different areas that need to be
  considered when changing to the OO approach.
  These are
• Tools The right programming environment,
  database and CASE tool need to be selected and
  implemented.
• Methodology The right methodology has to be
  selected and implemented.
• Organization The necessary training must be
  provided. Organizational impact must be assessed.
  A suitable pilot project must be selected. The
  change effort must be planned and managed and the
  right personnel must be available.

13
Preparing for your own change to OO Development

• The availability of well-qualified people would
  be a main bottleneck for an organization.
• Fundamental change in their way of thinking is
  required by people accustomed to structured
  system development.
• IT personnel with the right educational
  background might be able to compete successfully
  with more experience information system
  developers.

14
Is Everything an Object?

• Why Focus on Objects?
• What is an Object?
• What is an Object in a Computer System?
• Types of Objects in Computer Systems
• User interface Objects
• Operating Environment Objects
• Task-Related Objects

15
Why Focus on Objects?

• In some way everything can be an object.
• The classification process is based on the
  features and behaviors that make up a class of
  objects.
• A more specialized class inherits the features
  and behaviors of all classes above in a
  hierarchy.
• People naturally organize information into
  classes and hierarchies of general classes and
  more specialized subclasses --called
  Generalization/ Specialization hierarchies.
• People also naturally recognize that things can
  be divided into parts called whole-part
  hierarchies.

16
Why Focus on Objects?

• Generalization/Specialization hierarchies and
  whole-part hierarchies allow us to understand
  things and define things and communicate about
  things in terms of other things we know.
• Generalization/Specialization hierarchy is often
  described as a series of is a relationships.
• We also understand things, define things, and
  communicate about things by using the concept of
  an object and its parts.

17
Inheritance and Generalization/ Specialization
Hierarchies

• Generalization/ Specialization Hierarchies allow
  inheritance.
• We organize and define things and communicate
  about things in terms of Generalization/
  Specialization Hierarchies.
• Inherit means get something from, in OO approach
  one class of objects can inherit attributes and
  methods from another.
• OO approach encourages and allows reuse. Reuse
  means to use something over again, rather than
  having to reinvent the wheel.
• This method allows a more compact and less
  redundant model

18
Classification and Generalization

• Gen/Spec is a relationship between classes only
• There is no object relationship
• Bob calls his car Max.
• Max is a Ford Mustang.
• A Ford Mustang is a Car.
• Cars are Vehicles.
• Ford is a Make.

19
Why Focus on Objects

• The OO approach to computer system is therefore a
  more natural approach for people, since we
  naturally think in terms of objects, and we
  classify them into hierarchies and divide them
  into parts. Fig 2.3

20
What is an Object?

• A person or thing through which action, thought,
  or feeling is directed. Anything visible or
  tangible a material product or substance (Coad
  Yourdon, 1991, p. 52)
• James Martin defines an object in relation to
  concepts From a very early age, we form
  concepts. Each concept is a particular idea or
  understanding we have about our world. These
  concepts allow us to make sense of and reason
  about the things in our world. These things to
  which our concepts apply are called objects.
• ( Martin, 1993, p. 17).

21
What is an Object?

• Grady Booch uses a variety of approaches A
  tangible and/or visible thing something that may
  be apprehended intellectually something toward
  which thought or actions is directed. An
  individual , identifiable item, unit, or entity,
  either real or abstract, with a well-defined role
  in the problem domain. Anything with a crisply
  defined boundary. (Booch, 1994, p. 82)

22
What is an Object?

• Others conclude that anything can be considered
  an object An object is a thing that can be
  distinctly identified. At the appropriate level
  of abstraction almost anything can be considered
  to be an object. Thus a specific person,
  organization, machine, or event can be regarded
  as an object. (Coleman et el. 1994, p. 13)
• All of these definitions acknowledge that an
  object is something that people think about,
  identify, act upon or apply concepts to.
• And because different people have perceptions of
  the same object, what an object is depends upon
  the point of view of the observer. We describe
  an object on the basis of the features and
  behaviors that are relevant to us.

23
What is an Object in a Computer System

• Just about anything can be considered to be an
  object can be identified as an object in a
  computer system. In computer system it could be a
  menu or button.
• Peter Coad uses a concept he call object think,
  he simply proposes that an object simply knows
  things and knows how to do things.

24
A generalization/Specialization hierarchy of
types of objects in a computer system Fig 2.4
25
Types of objects in Computer System

• If anything can be considered to be an object at
  some level of abstraction then anything applying
  to computer systems can be considered to be an
  object.
• The types of objects in computer systems might be
  classified as user interface objects, operating
  system objects and task-related objects.

26
User Interface Object

• User interface objects are objects that
  physically appear on the screen and end-users
  directly interact with them.
• They have attributes, they exhibit behaviors,
  they interact with each other and most important
  we interact with them.
• When developers says they are using OO technology
  to develop a systems they really mean they are
  using interface objects to develop a graphical
  user interface for their system.

27
Common User Interface ObjectsFig 2.5
28
Operating Environment Objects

• Operating environment object is another type of
  object.
• Client and a Server in the client/server
  architecture is OO.
• A server object provides services for others and
  client object requests services form others.
• To those developer who works on Operating systems
  OO mean operating system objects.

29
Task-Related Objects

• Task-related objects are used to actually
  complete work. These things that a computer
  application deals with or creates.
• Document Objects documents are objects that know
  things and know how to do things. (i.e. word
  processing applications)
• Multimedia Objects Multimedia systems are
  another important type of application which
  contain sound, video, images.
• Problem Domain Objects They are things typically
  involved in information processing systems, such
  as customers, products, order or employees. They
  often correspond to the types of things
  identified when modeling data.

30
A multimedia object Fig 2.7