We Know Less Than You Think (But We Do Know Something)
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We Know Less Than You Think (But We Do Know Something)



A quick summary of empirical software engineering, followed by early results from a survey of how over 1900 scientists use computers in their research.

A quick summary of empirical software engineering, followed by early results from a survey of how over 1900 scientists use computers in their research.



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We Know Less Than You Think (But We Do Know Something) Presentation Transcript

  • 1. We Know Less Than You Think (But We Do Know Something) Copyright © 2009 Gregory V. Wilson. This presentation may be freely used and distributed with attribution. Prof. Greg Wilson Dept. of Computer Science University of Toronto [email_address]
  • 2. Computer “Science” (?)
    • Some of computer science is applied mathematics
    • But what kind of “science” is software engineering?
      • Most of it isn’t (yet?) as rigorous as bridge design
      • Practitioners would object to being called alchemists, organizational psychologists, or cheerleaders
    http://www.third-bit.com 00001
  • 3. Show Me
    • Shaw 1990: “Prospects for a Discipline of Software Engineering”
      • Called for evidence-based software engineering
      • Built on empirical work since the 1970s by Boehm, Basili, Glass, and others
    • Empirical studies now expected by top journals and conferences
    http://www.third-bit.com 00010
  • 4. There’s a Lot of Folklore…
    • “ The best programmers are up to 28 times more productive than the worst.” (or 40, or 100, or…)
      • Trace it back: [SAC68] had 12 (self-taught) subjects
    • [BOE75]: best to worst is a factor of 5
      • Borne out by other studies
      • Consistent with other fields
    http://www.third-bit.com 00011
  • 5. Non-Linearity
    • [WOO79]: 25% increase in problem complexity  100% increase in solution complexity
      • Interactions grow as N 2
    • This can work in your favor
      • Cut 1/4 of your features, problem because 1/2 as hard to solve
    http://www.third-bit.com 00100
  • 6. Glass’s Law
    • Any new tool or technique initially makes you less productive
      • Which is why so many senior students program with Notepad
    • [GLA99]: 5-35% improvement is the best you can expect from changing tools
      • Ah, but techniques…
    http://www.third-bit.com 00101
  • 7. Project Failure
    • #1 cause: poor estimation
      • Short iterations cure this in the small, but don’t help in the large
    • #2 cause: unstable requirements
      • But research code often doesn’t have “requirements”
    • See [VGE91], [COL95], [HOF01]
    http://www.third-bit.com 00110
  • 8. Boehm’s Curve
    • [BOE01] and many others
    http://www.third-bit.com 00111
  • 9. Re-Use
    • “ It takes three times longer to build a reusable component than it does to build something used only once.”
    • “ If more than 25% of a component has to be revised, it’s better to rewrite it from scratch.”
    • See e.g. [THO97]
    http://www.third-bit.com 01000
  • 10. Lines of Code
    • “ Productivity and reliability depend on the length of a program’s text, independent of language level.”
    • See [PRE00] for a recent experiment
    • However, machine-independent code has machine-independent performance
    http://www.third-bit.com 01001
  • 11.
    • “ Maintenance makes up 40-80% of the total cost of a software project.”
      • [BOE75] and many more since
    • But roughly 60% of “maintenance” is enhancement
    • And 30% of maintenance time is spent figuring out things work
    Maintenance http://www.third-bit.com 01010
  • 12.  
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  • 19.
    • Lack of documentation was the #1 complaint for over 40% of respondents, and in the top three for almost 80%
    • … but ranked second to last in list of where respondents spend their time
    What Hurts? http://www.third-bit.com 01010
  • 20.
    • Emphasis on grids and GPUs is inappropriate and unproductive
      • Improving skills will yield greater dividends on shorter timescales
    • swc.scipy.org for current course
      • software-carpentry.org for the next one
      • We’ll be webcasting July 13-31
    Thoughts http://www.third-bit.com 01011
  • 21. References
    • [BOE75] Boehm: “The High Cost of Software”
    • [COL95] Cole: “Runaway Projects—Causes and Effects”
    • [GLA99] Glass: “The Realities of Software Technology Payoffs”
    • [HOF01] Hofmann and Lehner: “Requirements Engineering as a Success Factor in Software Projects”
    • [PRE00] Prechelt: “An Empirical Comparison of Seven Programming Languages”
    • [SAC68] Sackman et al: “Exploratory Experimental Studies Comparing Online and Offline Programming Performances”
    • [THO97] Thomas et al: “An Analysis of Errors in a Reuse-Oriented Development Environment”
    • [VGE91] Van Genuchten: “Why Is Software Late?”
    • [WOO79] Woodfield: “An Experiment on Unit Increase in Problem Complexity”
    http://www.third-bit.com 01100
  • 22. Recommended Reading
    • Doar Practical Development Environments
    • Feathers Working Effectively with Legacy Code
    • Fogel Producing Open Source Software
    • Ford The Productive Programmer
    • Glass Facts and Fallacies of Software Engineering
    • Johnson GUI Bloopers
    • Kernighan almost anything
    • Kniberg Scrum and XP From the Trenches
    • Mak The Martian Principles
    • Nygard Release It!
    • Spinellis Code Reading and Code Quality
    • Weiner Time, Love, Memory
    01101 http://www.third-bit.com