Introduction to eXtreme Programming

Remko Popma Azzurri Ltd.

http://www.azzurri.co.jp

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Contents

• The problem – Problems in software development • eXtreme Programming (XP) – Values – Practices – Why XP works – Benefits of XP • Conclusions • Resources 2

Problems in software development

Risks: • Schedule slips • Business misunderstood • Defect rate • Project cancelled • System goes sour • Business changes 3

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 4

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 5

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 6

Project cancelled

Size of project

1 function point 10 function points 100 function points 1,000 function points 10,000 function points 100,000 function points Average

Early

14.68% 11.08% 6.06% 1.24% 0.14% 0.00% 5.53%

On-Time

83.16% 81.25% 74.77% 60.76% 28.00% 13.67% 56.94%

Delayed

1.92% 5.67% 11.83% 17.67% 23.83% 21.33% 13.71%

Cancelled 0.25% 2.00% 7.33% 20.33% 48.00% 65.00% 23.82% Table 1: Percentage of projects early, on-time, late, canceled (from Patterns of Software Systems Failure and Success, by Capers Jones) Sum

100.00% 100.00% 100.00% 100.00% 100.00% 100.00% 100.00% 7

Project cancelled

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

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 9

Business changes

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

Economics of software development

cost of change Requirements Analysis Design Implementation Testing Production

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What if…

cost of change Time

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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.

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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 14

XP values

• Communication • Simplicity • Feedback • Courage 15

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 16

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 17

Testing

• Unit Tests and Functional Tests • Test a little, code a little… – “Test-first programming” • Tests become the specification • Tests give confidence in the system • Tests give courage to change the system 18

Unit tests

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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 20

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) 21

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 22

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 23

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 24

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 25

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 26

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 27

Web resources

• www.junit.org

• www.xprogramming.com

• www.extremeprogramming.org

• www.refactoring.com

• www.pairprogramming.com

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• Questions?

Thank you

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