MANAGING COMPLEXITY

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MANAGING COMPLEXITY

• Lecture OO01
• Introduction to Object-oriented Analysis and
  Design
• Abstract Data Types

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References

• Booch, Object Oriented Analysis and Design, Chpt
  1
• Parnas, D.L.
• On the Criteria to be Used in Decomposing
  Systems into Modules, Comm. Of the ACM, Dec, 1972

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Teaching Points

• Three tools for coping with complexity
• Abstract Data Types and Modularization
• Information Hiding

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Review - Software is complex because

• complex problem domain
• difficult development process
• (large systems-gtlarge orgs)
• flexibility
• discrete systems

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How to Cope?

• Three Tools
• Decomposition
• Hierarchy
• Abstraction

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Decomposition

• breaks the problem into understandable components
• allows elements of an organization to work on
  small chunks of the system

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Decomposition

• can limit flexibility by producing well defined
  (possibly reusable) building blocks
• opens the possibility for separation of issues
  allowing isolation of the state space
• Coupling vs. Cohesion

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Hierarchy

• allows understanding of relationships between
  small numbers of components
• different kinds of hierarchies allow insight into
  different aspects of the complex system

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Abstraction

• probably the most important of the three tools
• the overlooking of unimportant detail
• concentration upon the essential features of an
  idea

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Abstraction Examples

• business organization chart
• virtual machine
• character based I/O
• graphics objects

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Recall Structured Analysis and Design

• Analysis/Design Strategy
• Decompose the problem into nested procedures
• Use the best algorithm you can find for the
  procedures

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Data Flow Diagram
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Must Reduce

• complexity
• vulnerability to change in design or requirement

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A New Modularization

• based on abstract data types (classes)
• encapsulation (data hiding)
• abstraction (interface)

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An Object

• An instance of an abstract data type
• State
• Behaviour
• Identity

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New Design Paradigm

• Set of Collaborating Objects

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Attributes of an Object-Oriented Environment

• Encapsulation
• Abstraction
• Modularity
• Hierarchy

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Teaching Points

• Three tools for coping with complexity
• Abstract Data Types and Modularization
• Information Hiding