Agile Methods and Extreme Programming

CS 414, Software Engineering I

Mark Ardis

Rose-Hulman Institute

December 19, 2002

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Outline

I. Origin of Agile Methods

II. Examples of Agile Methods

III. Extreme Programming

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I. Origin of Agile Methods

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First Cartoon of the Day

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Spectrum of Methods

Source: "Get ready for agile methods, with care" by Barry Boehm, IEEE Computer, January 2002.

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Boehm's Risk Exposure Profile

Source: "Get ready for agile methods, with care" by Barry Boehm, IEEE Computer, January 2002.

Black curve: Inadequate plans

Red curve: Market share erosion

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Safety-Critical Profile

Source: "Get ready for agile methods, with care" by Barry Boehm, IEEE Computer, January 2002.

Black curve: Inadequate plans

Red curve: Market share erosion

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Agile Profile

Source: "Get ready for agile methods, with care" by Barry Boehm, IEEE Computer, January 2002.

Black curve: Inadequate plans

Red curve: Market share erosion

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Agile Manifesto

• We are uncovering better ways of developing software by doing it and helping others do it. Through this work we have come to value: – Individuals and interactions over processes and tools

– Working software over comprehensive documentation

– Customer collaboration over contract negotiation

– Responding to change over following a plan

• That is, while there is value in the items on the right, we value the items on the left more.

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II. Examples of Agile Methods

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The List of Agile Methods

• Adaptive Software Development

• Crystal

• Dynamic System Development Method (DSDM)

• Extreme Programming

• Feature Driven Development (FDD)

• SCRUM

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Adaptive Software Development

Source: "Retiring lifecycle dinosaurs" by Jim Highsmith, Software Testing and Quality Engineering, July/August 2000

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Crystal

• "family of human-powered and adaptive, ultralight, 'shrink-to-fit' software development methodologies"

• People-centric

• Reduces bureaucracy to least practical

• Start small and make it smaller

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Dynamic System Development Method (DSDM)

Source: DSDM website

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Feature Driven Development (FDD)

• At start of project:– Develop an Overall Model– Build a Features List– Plan by Feature

• Within each iteration:– Design by Feature– Build by Feature

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SCRUM

Source: SCRUM website

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III. Extreme Programming

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Motivation

• Knobs on a control board

• Each knob a practice that works well

• Turn all knobs up to 10

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Learning to Drive

"Driving is not about getting the car going in the right direction.

Driving is about constantly paying attention, making a little correction this way, a little correction that way."

-- Kent Beck, Extreme Programming Explained

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Four Values

• Simplicity– create the simplest thing that could work

• Communication– face-to-face, not document-to-face

• Feedback– lots of tests

• Aggressiveness

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Four Basic Activities

• Coding– cannot do without it

• Testing– if it cannot be tested it doesn't exist

• Listening– to those with domain knowledge

• Designing– to keep the system from decaying

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Twelve Practices

7. Pair programming

8. Collective ownership

9. Continuous integration

10. 40-hour week

11. On-site customer

12. Coding standards

1. The Planning Game

2. Small releases

3. Metaphor

4. Simple design

5. Testing

6. Refactoring

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1. The Planning Game

• Business people decide:– scope– priority– release dates

• Technical people decide:– estimates of effort– technical consequences– process– detailed scheduling

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The Planning Game

• Collect User Stories on cards

• Stories are written by customers

• Stories generate tests

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Estimating

• Be concrete

• No imposed estimates

• Feedback: compare actuals to estimates

• Re-estimate periodically

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Scheduling

• Each story gets an estimate of effort

• Customers decide which stories are most important

• Programmers calculate how long each release will take

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2. Small Releases

• Every release should be as small as possible

• Every release has to completely implement its new features

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Waterfall to XP Evolution

Source: "Embracing change with extreme programming" by Kent Beck,IEEE Computer, October 1999.

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3. Metaphor

• Each XP project has its own metaphor– naive– system is a spreadsheet

• Metaphor replaces architecture as the view from 10,000 feet

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4. Simple Design

• Runs all the tests

• Has no duplicated logic

• States every intention important to programmers

• Has the fewest possible classes and methods

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5. Testing

• Any feature without an automated test does not exist.

• Programmers need confidence in correct operation

• Customers need confidence in correct operation

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Tools for Testing

• Test harnesses for various programming languages

• Simplify job of creating and running the tests

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6. Refactoring

• Always ask if there is a way to make the program simpler

• When the system requires duplication of code, it is asking for refactoring

• Can always find a series of small, low-risk steps

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Second Cartoon of the Day

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7. Pair Programming

• All code written with 2 people at one machine

• Driver:– thinks about best way to implement

• Passenger:– thinks about viability of whole approach– thinks of new tests– thinks of simpler ways

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Workspace

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8. Collective Ownership

• Anybody who sees an opportunity to add value to any portion of the code is required to do so

• Everyone knows something about everything

• Everyone feels obligated to make improvements

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9. Continuous Integration

• Integrate and test every few hours, at least once per day

• All tests must pass

• Easy to tell who broke the code

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10. 40-Hour Week

• People should be fresh and eager every morning

• Overtime is a symptom of a serious problem

• XP only allows one week of overtime

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11. On-Site Customer

• Real customer will use the finished system

• Programmers need to ask questions of a real customer

• Customer can get some other work done while sitting with programmers

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12. Coding Standards

• Everyone edits everyone's code

• Standard should require least amount of overhead

• Standard should be adopted voluntarily by the team

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How could this work?

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1. The Planning Game

• You couldn't start with only a rough plan

• Unless:– customers did updating based on

estimates of programmers– short releases (2) revealed any mistakes in

plan– customer was sitting with programmers

(11) to spot trouble

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2. Small Releases

• You couldn't release new versions so quickly

• Unless:– the Planning Game (1) helped work on the

most valuable stories– you were integrating continuously (9)– testing (5) reduced defect rate

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3. Metaphor

• You couldn't start with just a metaphor

• Unless:– you got feedback on whether metaphor

was working– your customer was comfortable talking

about the system in terms of the metaphor– you refactored continually (6) to refine

understanding

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4. Simple Design

• You couldn't have just enough design for today

• Unless:– you were used to refactoring (6)– you had a clear overall metaphor (3)– you were programming with a partner (7)

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5. Testing

• You couldn't write all those tests

• Unless:– the design was as simple as possible (4)– you were programming with a partner (7)– you felt good seeing all those tests running– your customer felt good seeing all those

tests running

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6. Refactoring

• You couldn't refactor the design all the time• Unless:

– you were used to collective ownership (8)– you had coding standards (12)– you programmed in pairs (7)– you had a simple design (4)– you had enough tests (5)– you had continuous integration (9)– you were rested (10)

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7. Pair Programming

• You couldn't write all the code in pairs• Unless:

– coding standards (12) reduced picayune squabbles

– everyone were fresh and rested (10)– the pairs wrote tests together (7)– the pairs had a metaphor (3) to ground their

decisions– the pairs were working within a simple design (4)

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8. Collective Ownership

• You couldn't have everyone changing everything

• Unless:– you integrated after a short time (9)– you had enough tests (5)– you programmed in pairs (7)– you adhered to coding standards (12)

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9. Continuous Integration

• You couldn't integrate every few hours

• Unless:– you could run tests quickly (5)– you programmed in pairs (7)– you refactored (6)

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10. 40-Hour Week

• You couldn't work only 40 hours/week

• Unless:– the Planning Game (1) were choosing the

most important work to do– you had enough tests (5) to avoid nasty

surprises– you were working at top speed already

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11. On-Site Customer

• You couldn't have a real customer sitting by the programmers full-time

• Unless:– they could produce value by writing

functional tests– they could produce value by making small-

scale priority and scope decisions

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12. Coding Standards

• You couldn't get everyone to use the same coding standard

• Unless:– they were part of a winning team by

practicing XP