The problem. extreme Programming (XP) Conclusions Resources. Problems in software development. Practices Why XP works Benefits of XP

Transcription

1 Introduction to extreme Programming

2 Contents The problem Problems in software development extreme Programming (XP) Values Practices Why XP works Benefits of XP Conclusions Resources

3 Risks: Problems in software development Schedule slips Business misunderstood Defect rate Project cancelled System goes sour Business changes

4 Schedule slips Many projects are not delivered on time Examples: Word 1.0, Netscape 6 Some deadlines cannot be moved Example: Y2K What if: most business value is delivered on time

5 Business misunderstood Without direct communication, developers have to guess what the customer wants. Example: The Orthodontics Project What if: an on-site customer steers development

6 Defect rate The software is put in production, but the defect rate is so high that it isn t used. What if: you have automated testing

7 Project cancelled Size of project Early On-Time Delayed Cancelled Sum 1 function point 14.68% 83.16% 1.92% 0.25% % 10 function points 11.08% 81.25% 5.67% 2.00% % 100 function points 6.06% 74.77% 11.83% 7.33% % 1,000 function points 1.24% 60.76% 17.67% 20.33% % 10,000 function points 0.14% 28.00% 23.83% 48.00% % 100,000 function points 0.00% 13.67% 21.33% 65.00% % Average 5.53% 56.94% 13.71% 23.82% % Table 1: Percentage of projects early, on-time, late, canceled (from Patterns of Software Systems Failure and Success, by Capers Jones)

8 Project cancelled What if: short releases deliver at least some useful working software, reflecting investment to date

9 System goes sour Software is put into production successfully, but after a couple of years the cost of making changes or the defect rate rises so much that the system must be replaced. What if: the design is simple and the code quality is high

10 Business changes New laws, market changes: business priorities change What if: the customer can change their mind, substitute functionality, and change priorities

11 Economics of software development cost of change Requirements Analysis Design Implementation Testing Production

12 What if cost of change Time

13 extreme Programming A system of practices that a community of software developers is evolving to address the problems of quickly delivering quality software, and then evolving it to meet changing business needs.

14 extreme Taking proven practices to the extreme If testing is good, let everybody test all the time If code reviews are good, review all the time If design is good, refactor all the time If integration testing is good, integrate all the time If simplicity is good, do the simplest thing that could possibly work If short iterations are good, make them really, really short

15 XP values Communication Simplicity Feedback Courage

16 XP practices The Planning Game* Small Releases Metaphor Simple Design* Testing* Refactoring* Pair Programming* Collective Ownership Continuous Integration 40-Hour Week On-Site Customer Coding Standards Open workspace Daily Schema migration

17 The Planning Game Business writes a story describing desired functionality Stories are written on index cards Development estimates stories Velocity determines number of stories per iteration Business splits and prioritizes stories and determines the composition of releases Velocity is measured and adjusted every iteration Customer steers development

18 Testing Unit Tests and Functional Tests Test a little, code a little Test-first programming Tests become the specification Tests become the specification Tests give confidence in the system Tests give courage to change the system

19 Unit tests

20 Pair Programming Two people looking at one machine, with one keyboard and one mouse Two roles: implementation and strategy All production code is written in pairs

21 Pair Programming Benefits 15% less output than 2 solo programmers Continuous code review: better design, fewer defects Confidence to add to or change the system Discipline to always test and refactor Teach each other how the system works (reduced staffing risks) Learn from partner s knowledge and experience (enhances technical skills)

22 Simple design Do the simplest thing that could possibly work Passes all the tests No duplicate code States every intention Fewest possible classes and methods

23 Refactoring Design becomes everybody s daily business Continuously improve quality of the code Unit Tests and Pair Programming give courage Result: Fast development speed Code becomes easy to change

24 Why XP works Light-weight: discipline without bureaucracy Under stress, people do what is easiest All XP practices have short-term benefits as well as long-term benefits Development as a Conversation The code is the documentation XP is fun

25 Who benefits from XP? Programmers: get clear requirements & priorities can do a good job can make technical decisions don t work overtime Customers: get most business value first get accurate feedback can make informed business decisions can change their mind

26 Conclusions Use XP on projects with vague or changing requirements with small teams XP works, and is very fast XP is fun to execute At Azzurri, we use XP as much as possible with clients, and exclusively for internal projects

27 XP books and papers Extreme Programming Explained Kent Beck Refactoring Martin Fowler Planning Extreme Programming Kent Beck et al Extreme Programming Installed Ron Jeffries et al Extreme Programming Examined Giancarlo Succi et al Extreme Programming in Practice Robert C. Martin et al Extreme Programming Explored William C. Wake Extreme Programming Applied Ken Auer et al The Costs and Benefits of Pair Programming Alistair Cockburn et al

28 Web resources

29 Thank you