CMPUT 301: Lecture 02 Basic concepts of Design and Implementations

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CMPUT 301 Lecture 02 Basic concepts of Design
and Implementations

• Lecturer Martin Jagersand
• Department of Computing Science
• University of Alberta
• Notes based on previous courses by
• Ken Wong, Eleni Stroulia
• Zach Dodds, Martin Jagersand

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Goals today

• Concepts and stages in the program designs and
  implementation process.
• How and why Object Oriented design and
  Programming evolved and where it fits in the
  greater picture of SwEng paradigms.
• Some practical OO concepts and examples.

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Design strategies overview

• Previous courses learned pragmatics of
  programming and principles of algorithms
• This course Focus on whole project design.
• Important concepts
• abstraction(simplifying to its essentials the
  description of a real-world entity)
• separation(treating what and how aspects
  independently)

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Abstraction

• Examplessales person, medical patient, etc.

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Abstraction

• Design strategy 1
• focus on the essential aspects of an entity or
  concept
• ignore or conceal non-essentials
• map real-world entities to software objects
• Abstraction
• a named collection of attributes (data) and
  behavior (actions, methods) relevant to modeling
  a given entity for some particular purpose

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Separation

• Design strategy 2
• separate what is to be done from how it is
  done
• separate design issues from implementation
  details
• separate externally visible behavior
  (interfaces) from hidden, internal mechanisms
  (implementations)

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Interchangeable Implementations
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Interchangeable Implementations
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Separation

• Separation of concerns
• interfaces reveal assumptions
• implementations hide changeable details
• interface contract
• avoid ripple effects

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Design concepts vs.programming languages

• Note that design concepts (e.g. abstraction,
  separation ) are independent of programming
  languages
• But one or several programming language may
  support or impose certain concepts.
• Example Separation
• .h files in c
• Definition modules in modula 2,3
• Interfaces in java

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Programming languages

• Programming paradigms and languages are between
  (and link) human concepts and ideas to machine
  implementations
• Have changed during time (more so than either
  ideas or machines)

Prog. Lang.
Computer
Human ideas
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Evolution of programming languages

• Machine lang
• Imperative (Fortran, c, Pascal)
• Functional (lisp, ML, Haskell)
• Logical (prolog, alf)
• Object Oriented (Smalltalk, c, java)

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Design Strategies vs.programming languages

• Note again that design strategy (e.g.
  abstraction, separation ) are independent of
  programming languages.
• Also The same project can be implemented using
  different strategies (and languages)

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Example Higher order functions

• Concept from functional design paradigms and
  mathematics
• Qf g
• Implementation in imperative and OO languages and
  comments.
• (blackboard)

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Example XVision

• Provides visual tracking (rmember interaction
  video in last lecture)
• 10 years effort several people, several univ
• Several implementations, same functionality
• Xvision 1-1.3 (Upenn, Yale) c, c, Imperative
• fVision (Yale) Haskell, greencard, c
• XVision2 (JHU) c
• (Written using some fvision design strat)

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Xvision application face tracking
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Xvision 1-1.3 (Upenn, Yale) c, c, Imperative

• Written by hackers
• Neat tricks speed up, but shortcut across
  abstractions
• Good to provide specified functionality,
• but hard to port
• Hard to extend

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fVision (Yale) Haskell, greencard, c
Example program
trackMouth v bestSSD mouthIms (newsrcI v
(sizeof mouthIms)) trackLEye v bestSSD leyeIms
(newsrcI v (sizeof leyeIms)) trackREye v
bestSSD reyeIms (newsrcI v (sizeof
reyeIms)) trackEyes v composite2 (split, join)
(trackLEye v) (trackREye v) where split
segToOrientedPts --- some geometry join
orientedPtsToSeg --- some more
geometry trackClown v composite2 concat2
(trackEyes v) (trackMouth v)
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fVision (Yale) Haskell, greencard, c

• Uses dataflow model, higher order functions
• Much easier to script new behaviours
• Easier to express geometry
• More compact code
• Haskell code about speed about ¼ of c

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XVision2 (JHU) c

• See it in our lab, use in c306, learn in c610!
• Designed first, then implemented
• Extensible, portable
• Some loss of neat speadups due to separation
  and hiding
• Speed ¼ - 1/7 of original c version.

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Next time

• Object oriented design strategies