CMPUT 301: Lecture 02 Basic concepts of Design and

Implementations

Lecturer: Martin JagersandDepartment of Computing Science

University of Alberta

Notes based on previous courses byKen 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

• Examples:sales 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)

Computer

Human ideas

Prog.

Lang.

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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

• Q=f 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

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 geometrytrackClown v = composite2 concat2 (trackEyes v) (trackMouth v)

Example program:

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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