SOEN 343 Software Design

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SOEN 343Software Design

• Section H Fall 2006
• Dr Greg Butler
• http//www.cs.concordia.ca/gregb/home/soen343h-f0
  6.html

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Outline

• GoF Design Patterns
• Adapter, Façade, Strategy, Observer
• Design Review

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GoF Pattern Summary Relationships
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GoF Pattern Classification

• Behavioral Patterns
• Creational Patterns
• Structural Patterns

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GoF Behavioral Patterns

• Chain of Responsibility
• Command
• Interpreter
• Iterator
• Mediator
• Memento

• Observer
• State
• Strategy
• Template Method
• Visitor

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GoF Creational Patterns

• Abstract Factory
• Builder
• Factory Method
• Prototype
• Singleton

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GoF Structural Patterns

• Adapter
• Bridge
• Composite
• Decorator
• Facade
• Flyweight
• Proxy

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Adapter

• Context / problemHow to resolve incompatible
  interfaces, or provide a stable interface to
  similar components with different interfaces?
• SolutionConvert the original interface of a
  component into another interface, through an
  intermediate adapter object.

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Adapter

• Suppose we have a tax calculation class (or
  external library) but the interface is not well
  suited for our application.

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Adapter

• Adapter providesan interface suitedto the
  application

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Adapter (For More than One Class)

• What if more than one class (library) needs to be
  adapted?

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Adapter
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Facade
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Facade
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Strategy

• Context / problemHow to design for varying, but
  related, algorithms or policies? How to design
  for the ability to change (even dynamically)
  these algorithms or policies?
• SolutionDefine each algorithm/policy/strategy
  in a separate class with a common interface

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Strategy
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How Do We Create a Strategy?
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Observer Pattern
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Observer

• How shall we have the display be updated?
• Why not have the Sale inform the display when
  it changes value.

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What is Wrong With This?
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Observer Pattern

• Context / ProblemDifferent kinds of subscriber
  objects are interested in the state changes or
  events of a publisher object, and want to react
  in their own way when the publisher generates the
  event.

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Observer Pattern

• SolutionDefine a subscriber or listener
  interface. Subscribers implement this interface.
  The publisher can dynamically register
  subscribers who are interested in an event, and
  notify them when an event occurs.
• Clarification Publisher can dynamically process
  registration requests from subscribers.

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Observer Pattern (GoF book)
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Observers Illustration
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Sale Example
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Recall

• Way back in week 5 we asked the question
• How do I come up with a design?

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How Do I Come Up With a Design?

• What are the inputs to the activities of design?
• What are the outputs?

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Design Activities Inputs Outputs

• Product requirements
• Project plan

• Architectural factors
• ArchitectureDocument
• Architectural Style(s)

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Design Input SRS

• What is contained in the SRS?(name some of its
  parts)

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Design From SRS to ...

• Domain Model
• Use Case Model

• Design Model
• Control Style / Pattern
• User-interface design

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Design Model Classes

• Domain Model often used as first approximation to
  Design Model.
• Domain Model contains
• Conceptual classes
• Conceptual classes used as basis for similarly
  named design classes.
• (E.g. Larman, Chapter 16, p. 222.)

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EA Patterns
Template View
Page Controller
Presentation
Front Controller
Transform View
Domain Model
Transaction Script
Domain
Data Mapper
Table Module
Active Record
Row Data Gateway
Table Data Gateway
Data Source
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Enterprise ApplicationsDomain Model

• Requirements Domain Model

• Design Model classes Domain Model pattern

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From Requirements to Design

• Requirements artifacts e.g.
• Domain Model
• Use Case Model

• Design artifacts e.g.
• Software Architecture Document
• Design Model
• User-interface design

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Conceptual Classes to Design Classes

• Domain Model pattern

• Domain Model pattern

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Representational Gap

• Larman, Section 17.2
• The object developer has taken inspiration from
  the real-world domain in creating software
  classes. Therefore, the representational gap
  between how stakeholders conceive the domain, and
  its representation in software, has been lowered.

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From Rich Conceptual Domain Model to Rich set of
Domain Model classes