The document discusses the state of software engineering, highlighting the need for empirical evidence-based practices and addressing common misconceptions. It emphasizes issues like poor estimation, unstable requirements, and the high costs associated with software maintenance. Additionally, it critiques the effectiveness of certain development techniques and tools while underscoring the importance of improving skills over reliance on technology.

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

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