An Engineering Interlude

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An Engineering Interlude
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Santa Maria Del Fiore

• Designed by Fillipo Bruneleschi
• The marble slab inside reads
• Corpus Magni Ingenii Viri Philippi Brunelleschi
  Fiorentini
• (Body of the great and clever man Filippo
  Brunelleschi of Florence)

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• Ingenere is the Italian word for engineer
• Genius, ingenius, and ingenere clearly all have
  the same Latin root
• Builders of machines were clever
• In fact, Brunelleschi was awarded the dome
  contract but refused to divulge the design
• Typical of his day architecture was an exercise
  in cleverness

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• How does a profession differ from a craft?
• Substitution of standard techniques for
  cleverness
• Licensing
• Self-regulating professional bodies
• Government regulation
• Threat of litigation

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• Software Design
• Still in the craft (clever) stage

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Issues

• Not good enough for a program to run
• It must
• Be maintainable
• Communicate with other programs

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Software Development

• Assess client needs.
• Develop conceptual documentation
• Show to client. If not OK, go to step 1
• Build prototypes.
• Show to client. If not OK, go to step 1
• System design
• Program
• Test Components. If not OK, go to step 7
• Integrate Components.
• Test Integration. If not OK, go to step 6.

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Object-Oriented Design

• Goals
• Manage Complexity
• Promote software reuse
• Tools
• Data hiding
• Inheritance
• Composition
• Polymorphism

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A Quick How-To

• Object-Oriented Analysis
• Statement of what our client wants
• Object-Oriented Design
• How to provide it using OO tools

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Tasks

• Provide a problem statement (requirements
  analysis)
• Multiple discussions with client
• Determine objects needed to implement the system
• Look for nouns in problem statement
• Determine object attributes
• What do I know?
• How are the nouns described?
• These become the class variables
• Determine object behaviors
• What can I do?
• Look for verbs in problem statement
• These become the class methods

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Key Rule

• Information Hiding
• Though objects know how to communicate with one
  another across well-defined interfaces, objects
  are normally not allowed to know how other
  objects are implemented

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Unified Modeling Language

• OOD Tool
• We use C to communicate our instructions to a
  computer
• Designers use UML to communicate their
  instructions to those who will do the coding
• Important names
• Grady Booch
• James Rumbaugh
• Ivar Jacobsen
• All worked at Rational Software in the late 90s
• Adopted by the Object Management Group
  (www.omg.org) in 1997.
• OMG is a non-profit organization that promotes
  the development of standards in OO technology.
• OMG now has responsibility for maintaining the
  notation.
• UML 2.0 is the current version

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Sample Problem

• Develop software to perform ATM transactions.
  The software should model the functions of all
  hardware associated with an ATM, but not be
  concerned with how the hardware works. The ATM
  must authenticate a user and then perform a
  number of transactions. The user enters security
  a five digit account number through a numeric
  keypad. Choices are displayed, menu fashion, on
  the screen. The user enters the choice (balance,
  withdraw, deposit, exit) using the numeric
  keypad. The machine has a cash dispenser that
  dispenses bills in multiples of 20. The deposit
  slot receives deposit envelopes. If the user
  chooses to withdraw, he/she is presented with a
  screen indicating valid withdrawal amounts menu
  fashion (20,40,60,100,200, Cancel).
• There are several error conditions
• Invalid account number
• Invalid transaction choice
• Invalid withdrawal choice
• Withdrawal amount exceeds balance
• In case of error, the user receives an
  appropriate message and is invited to try again
  or quit.

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Class Diagram
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Class Diagram with Attributes and Methods