CSC223 2004F, Class 14: Exterme Programming (1)

Admin:
* No quiz!  (Would have been "What is the purpose of the driving story" or "What are the four values?")
* Questions on homework?  Note you will present your designs a week from today.
* ACM Brochures
* Math/CS lunch (every Monday, Cowles)
* Missing: Petersen
* Questions on reading?

Overview:
* Context: Kinds of programs.
* Context: Heavyweight models, generalized
* Beck's rhetorical strategy?
* Introduction to XP

/Context: Kinds of Programs/

* We don't talk about "real world" program development at Grinnell (at least not much)
* Different kinds of models:
  * General-purpose programs (Word processors, Spreadsheets, Macro recordes, etc.)
  * Special-purpose programs (niche programs): Designed for a specific market or problem, but will be sold to many people (Medical billing software, Lawyer's accounting software and time-recording software)
  * Custom software: Build for one customer according to his/her specifications
* An awful lot of proramming is custom or niche software

/Context: How to develop software?/

* Most traditional method: Anarchy
* Alternate traditional method: Super-programmer
* Traditional methods: Waterfall (heavyweight)
  * Many parts
    * Analysis
    * Specification 
    * Design
    * Implementation
    * Testing
    * Release
  * Each part completed before the next part is started
* Benefits?
  * Customer gets what (s)he/it originally contracted for
  * The "large scope" view helps avoid conflicts in integration
  * Coding should be straightforward
  * All questions are answered by the specification document
* Drawbacks?
  * Seems like some steps could be integrated
  * Customers change requirements
  * Long time to release
  * False sense of progress (you do sometimes have to backtrack)
  * Danger of unpredicted problem at a later stage requiring signficant reworking of earlier stage
  * Prediction can be hard
  * Testing tends to slip

/Beck et al. present an alternative: Lightweight programming/

* Small steps
* Lots of feedback between stages
* XP is *a* lightweight programming strategy; there are others
* Who is Beck's audience?  (Who are Beck's audiences?)
  * Professional programmers
    * Want evidence that it works
    * Want to know the impact on their lives
    * Are likely to think "Yeah, this is good, it's what I do anyway"
  * Managers of programmers 
    * Want evidence that it works
    * Does it address the problems we have with our current development strategy?
    * "It's what the programmers want to do; it must be wrong."
  * Business managers: Non-technical
    * Can I read it in less than an hour?
* Opponents of XP say "it's an attempt to call hacking software design"
* What rhetorical strategies does he use to address these audiences?
  * Claimed overall rhetorical structure for book: 
    * Part one: Analysis/Specification "The Problem"; Demonstrate that traditional software design has problems
      * Criteria for evaluating solutions
    * Part two: Design "The Solution"; Show that XP solves this problem.
    * Part three: Implementation "The Implementation"; How to do XP
    * Testing left to after release
  * Part one does discuss problems, part two does discuss solutions, part three does discuss implementation
  * However, he inserts aspects of the solution in part one, and aspects of the implementation in parts one and two
  * Tell stories (show that he relates; show successes)
  * "Layers": Lay out basic ideas and then look in depth at each one ("Tell 'em what you're going to say, say it, and tell 'em what you said)
  * Repetition and extension: He starts with one "raw material" and gradually adds to it

/Following that Rhetorical Structure/

* The driving metaphor
  * "Change is the only constant"
  * You can't just point your car and go; you need to adjust regularly
  * You drive through lots of small tweaks rather than big adjustments
  * Why does/should this metaphor apply to software?  The customer is the road.
* Four values for programmers and teams
  * Communication
  * Simplicity 
  * Feedback
  * Courage: Willingness to take risks
* What other values might be important?
  * Flexibility (implicit in communication, feedback, and courage)
  * "Write good code": Correctness (implicit in simplicity)
  * Teamwork (implicit at the deepest level)
* WARNING!  XP has not been formally verified (as far as I know)
* WARNING!  XP does not necessarily work for other kinds of development (those outside of software)
* DETOUR: The Waterfall model is a traditional engineering model.

Coming wednesday
* These values "suggest" particular principles
* XP is a set of practices which align well with these principles