overview about Design pattern , and the impact of design pattern on the software quality

1. Impact of Design Pattern on
Software Quality
Omar Adnan Isaid

2. Agenda
• What is Software Quality ?
• What is Design Pattern ?
• Gang of Four (GoF).
• Design Pattern Elements (Explained by Façade
Design Pattern).
• Advantages of Design Patterns.
• Strategy Design Pattern (Explained by Duck
Game).
• Auto Dynamic Difficulty Framework.

3. What is Software Quality ?
• ISO 9126: Software quality characteristic is a set of
attributes of a software product by which its quality is
described and evaluated".
• German Industry Standard DIN 55350 Part 11: Quality
comprises all characteristics and significant features of
a product or an activity which relate to the satisfying
of given requirements".
• ANSI Standard (ANSI/ASQC A3/1978): Quality is the
totality of features and characteristics of a product or a
service that bears on its ability to satisfy the given
needs".

4. What is Design Pattern?
• Design pattern is a solution for a repeatable
problem in the problem design.
• A design pattern isn't a finished design that
can be transformed directly into code.
• A design pattern is a description or template
for how to solve a problem that can be used
in many different situations.

5. Gang Of Four (GoF)
• GoF are Erich Gamma, Richard Helm, Ralph
Johnson and John Vlissides
• GoF are documented 23 classic software
design patterns in their book : Design
Patterns: Elements of Reusable Object-
Oriented Software.
• The GoF book first published at October 1994
and documented design patterns already exist
but not documented before.

6. Design Pattern Elements

7. Name element
[1] Name: Short ,Comprehensive ,No more than
two words.
• The meaning of the word Façade in oxford
dictionary "The principal front of building that
faces to a street or open space".
• The term Façade strongly related to the goal
of the Façade design pattern, which is to
provide a unified interface for different
subsystems of a system.

8. Design Pattern Problem
[2] Problem
• The suitable situation to apply the design
pattern.
• The preconditions must be available before
the designer decides to apply certain design
pattern.
• the design pattern can clarify the structure of
the inflexible designs of certain problems.

9. Façade Design Pattern Problem
• Suitable situation : when a unified interface is needed
to decouple different subsystems of a complex system.
• Preconditions before apply Façade Design Pattern
1. A simple interface can be applied to access different
subsystems of a system.
2. The development of the system will provide tightly
coupled system.
3. Each subsystem can have an interface, which can be
accessed using Façade design pattern interface.
• Inflexible to apply the Façade design pattern if it will
act as a bottleneck and limit the features of the system.

10. Design Pattern Elements
• [3] Solution
• Refers to the description of the problem
solution and the arrangement of the
elements.
• The element for the problem’s solution is the
class.

11. Design Pattern Solution

12. Façade interface

13. Façade interface can access any
subsystems

14. Advantages Of Design Patterns
[A] The Design patterns document the efforts of
the experts , who did their best efforts to
provide flexible and reusable software.
[B] The Design Pattern concerns with a flexible
software architecture.
The points [A] & [B] implies a set of advantages
for the developers, designers and others.

15. Advantages Of Design Patterns
• The Design Patterns provide a set of
advantages for the developers and designers
1. Not to reinvent the wheel.
2. Trade off between different solutions for the
same problem(Get the right pattern faster).
3. Studying the design patterns improves the
experience and knowledge of novices.

16. Strategy Design Pattern
• Assume the scenario where a certain game
has different types of ducks.
• The ducks in the game are different in their
sound and behavior.
• Not all the ducks have the same way of flying
or have the same sound.

17. Duck Hunt! NES 1984

18. Inheritance Solution

19. Override subclass methods

20. Disadvantages of Duck Inheritance
• If the Duck superclass has a lot of subclasses
serious disadvantages can be emerged
• For example, if the Duck superclass has 50
subclasses , where each Duck has a different
voice and behavior .
• The developer must override 100 methods
making some bugs in the road.
• At least some methods for different subclasses
may be modified from time to time.

21. Interface Design

22. Problems of Interface Design
• The interface design eliminates the overhead of
override the frequently changed methods of the
superclass Duck.
• If the mallard and red head ducks have the same fly
and sound behaviors , then the code of fly and sound
methods for the MallardDuck and RedheadDuck
classes are duplicated.
• The inheritance design means to modify methods from
time to time .But, interface design causes code
duplication , which is maintenance problem!
• No code reuse

23. The Strategy Design Pattern Solution
Take the parts that vary and
encapsulate them so that later you
can alter or extend the parts that
vary without affecting those that
do not

24. Interchangeable algorithms
• The Duck behavior (sound or fly) can be
described as set of interchangeable
algorithm.
• For example the algorithms for the sound
behavior can be quack , squeak or mute
• The algorithms are interchangeable because
the Duck sound can one of them.

25. Strategy Design Pattern

26. Implementing Fly and Sound
Algorithms

27. Advantages of the Strategy Design
• Reusability : Objects can use fly , quack
behaviors because these behaviors are not
hided anymore in the Duck superclass
• Maintainability : Modify existing behaviors
without make any modifications on the
subclasses of the Duck superclass

28. Medal of Strategy Pattern

29. Pattern Coupling (McNatt et. al,2011)
• The system architecture can be viewed as a
set of design patterns connected together.
• The coupled design patterns is a pair of design
patterns connected together using common
classes.

30. Types of Coupling
1. Tight Coupling
2. Loose Coupling

31. Tight Coupling
• The common classes strongly connected the
design pattern couple.
• Tight coupling leads to a large block of code.
• Any modification in the design pattern couple
can have a serious cost.

32. Loosely Coupling
• The common classes loosely connect the
design pattern couple.
• This type results in a maintainable and
reusable design pattern couple.

33. Overlapping Of Abstract Factory and Visitor Patterns

34. Auto Dynamic Difficulty Framework
• The ADD is framework to change the game
experience to match the player experience.
• The reusing of the ADD design patterns
eliminates the waste of cost and time to
create the ADD game-by-game