Quality - Douglas Crockford
- 1. Quality Douglas Crockford Yahoo! http://www.crockford.com/codecamp/quality.ppt
- 2. The Software Crisis The topic dominated the computer industry trade press for about a decade.
- 3. The Software Crisis Over budget Over time Unreliable Requirements not fully met Unmaintainable Failure Insecure (New!)
- 4. Software Crisis Year 45 It is old news, so no one talks about it In other news, the Sun will exhaust its supply of Hydrogen
- 6. Computer Science has not taught us how to manage software projects
- 7. Software Construction In some ways like any other sort of construction. In some ways radically different.
- 8. The Nature of Software Software is powerful and malleable That is its blessing That is its curse
- 9. Programming is Difficult Software is the most complicated stuff that humans make
- 10. Lack of metrics Measure of quality or completeness
- 11. Lines of Code Not an indicator of quality Not an effective measure of completeness Estimation is difficult
- 12. Programmers are optimists They wouldn't be able to do this work if they were not
- 13. Programmers do not understand how they spend their time They think they mostly are typing programs Mostly they are in meetings or technical conversations Or staring at the screen saying "My God. What have I done?"
- 14. Programmers do not understand how they spend their time Programmers tend to be skeptical of process improvements that might require more keystrokes. First Rule of Optimization: Optimize the process that is taking the most time.
- 15. Programming is a social activity Solo projects are the exception
- 16. Cost of Innovation Doing what has been done before v Doing what has not been done before
- 17. Legacy In other industries, the wealth of practice and tradition In software, past accomplishments are considered a liability The age at which programs become legacy is getting younger and younger Some programs become legacy before they are finished
- 18. Leaps Software is not governed by Moore's Law Software is governed by Murphy's Law Software leaps tend to come at 20 year intervals, not 2 year intervals Cycle of software generation closely related to cycle of human generation.
- 19. Leaps Leaps make it possible to implement projects of greater complexity. Adoption of leaping software technologies tends to be very slow. Controversy. Reluctance.
- 20. Leaps Plugboards
- 21. Leaps
- 22. Leaps Plugboards Symbolic Assembly Language
- 23. Leaps Plugboards Symbolic Assembly Language High Level Languages
- 24. Leaps Plugboards Symbolic Assembly Language High Level Languages Structured Programming
- 25. Leaps Plugboards Symbolic Assembly Language High Level Languages Structured Programming Object Oriented Programming
- 26. Object Oriented Programming 1967 Simula 1972 Kay begins Smalltalk 1980 Smalltalk released 1985 C++ Programming Language 1995 The Java Programming Language 2004 PHP 5
- 27. Leaps Plugboards Symbolic Assembly Language High Level Languages Structured Programming Object Oriented Programming Distributed Programming
- 28. Failed Leaps Artificial Intelligence Fifth Generation Languages Computer Aided Software Engineering Subjective-oriented, etc.
- 29. Software does not have enough self awareness to be afraid of bugs. That's why it works as well as it does.
- 30. Bugs Mr Edison, I was informed, had been up the two previous nights discovering a bug in his phonograph. Pall Mall Gazette , 1889-03-11
- 32. Snake Oil Silver Bullets
- 33. Mythical Man Month (1975) Fredrick Brooks "Adding manpower to a late software project makes it later." Second System Effect Prototyping (software is like waffles) "A project becomes a year late one day at a time."
- 34. Literate Programming Donald Knuth Programs are designed to be read. The program is the specification and documentation.
- 35. Incrementalism
- 37. Winchester House
- 38. Winchester House
- 39. Winchester House
- 40. Application Triad Skill Training and experience Technology Work with technology providers and standards bodies Requirements Better understanding of the impact of requirements determination and crisis
- 42. Mr Blandings Builds His Dream House (1948) Best movie ever about project management Blandings's problems: Lack of knowledge of technology Poor control over requirements
- 43. Feature Cost Development Time Deployment Cost Maintenance Cost (bloat, cruft) Download Time User Confusion/Training Bug Delivery
- 44. Code Value A significant fraction of our valuation is the state of our codebase. A low quality codebase is a liability.
- 45. Code Quality Microview: Coding Conventions Macroview: Program Architecture
- 46. The simplest thing we can do to enhance the value of our codebase is to make our programs readable.
- 47. Distinguish Invocations return(value); if(blah) foo (wah) function(){} return value; if (blah) foo(wah) function () {}
- 48. Programs are a medium of intentional communication Communicating detailed instructions with the machine Communicating with your development community Communicating with yourself
- 49. Good architecture is necessary to give programs enough structure to be able to grow large without collapsing into a puddle of confusion
- 50. Changing a correct program into another correct program.
- 51. Cruft Software Scar Tissue
- 52. Causes of Cruft Premature optimization Inexperience Misread source Feature enhancement Death March
- 55. Good secure programming is good programming.
- 56. As cruft accumulates, complexity grows, progess slows. Eventually, the codebase itself becomes a huge source of friction
- 57. Refactoring The process of code refinement. Correction of formatting. Insertion of documentation. Removal of cruft and bloat. Restructuring.
- 58. Plant and harvest your crops for six years, but let the land rest and lie fallow during the seventh year Exodus 23:10-11
- 59. Sometimes the best course is to start over
- 60. The Pain of the Crash Loss of a week's work, a day's work, an hour's work, is unbearable.
- 61. The illusion of completion "It's in the can."
- 62. An experienced team can cross that ground again very quickly. Focus must be on simplicity to avoid the second system effect.
- 63. Have regular code readings. Don’t wait until release to do code reviews. Do team code reading regularly during development. Problems can be discovered early. Good techniques can be shared early. Experienced developers can lead by example. Novice developers learn from the group.
- 64. Have regular code readings. Frequent. Helpful. Respectful.
- 65. Conclusion Quality First. Quality Last. Readable Code. Code Reading. Invest in the quality of your code base. Invest in your programmers and managers. Quality is the most important feature.