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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

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Problems in software development

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

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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

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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

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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

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Project cancelled

Size of project Early On-Time Delayed Cancelled Sum

1 function point 14.68% 83.16% 1.92% 0.25% 100.00%

10 function points 11.08% 81.25% 5.67% 2.00% 100.00%

100 function points 6.06% 74.77% 11.83% 7.33% 100.00%

1,000 function points 1.24% 60.76% 17.67% 20.33% 100.00%

10,000 function points 0.14% 28.00% 23.83% 48.00% 100.00%

100,000 function points 0.00% 13.67% 21.33% 65.00% 100.00%

Average 5.53% 56.94% 13.71% 23.82% 100.00%

Table 1: Percentage of projects early, on-time, late, canceled (from Patterns of Software Systems Failure and Success, by Capers Jones)

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Project cancelled

• What if:

short releases deliver at least some useful working software, reflecting investment to date

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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

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Business changes

• New laws, market changes: business priorities change

• What if:

the customer can change their mind, substitute functionality, and change priorities

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Economics of software development

Requirements Analysis Design Implementation Testing Production

cost of change

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What if…

Time

cost of change

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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

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XP values

• Communication

• Simplicity

• Feedback

• Courage

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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

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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

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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

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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

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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)

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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

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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

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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

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Who benefits from XP?

• get clear requirements & priorities

• can do a good job• can make technical

decisions• don’t work overtime

• get most business value first

• get accurate feedback• can make informed

business decisions• can change their mind

Programmers: Customers:

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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

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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 Cockbur

n et al

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Web resources

• www.junit.org

• www.xprogramming.com

• www.extremeprogramming.org

• www.refactoring.com

• www.pairprogramming.com

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Thank you

• Questions?