•     •   9 min read

Extreme Programming (XP): Not for
the Faint of Heart

Extreme Pro­gram­ming (XP) is an agile soft­ware devel­op­ment method­ol­o­gy. Like oth­er agile method­olo­gies, XP has its unique tools, process­es, and roles. The cre­ator of XP, Amer­i­can devel­op­er Kent Beck, did­n’t invent any­thing entire­ly new but instead took the best prac­tices of agile devel­op­ment and ampli­fied them to the extreme, hence the name Extreme Programming.

The method­ol­o­gy’s author, Kent Beck, led the Chrysler Com­pre­hen­sive Com­pen­sa­tion Sys­tem project in the late 90s, where he first applied XP prac­tices. He doc­u­ment­ed his expe­ri­ence and the cre­at­ed con­cept in the book Extreme Pro­gram­ming Explained,” pub­lished in 1999. This book was fol­lowed by oth­ers detail­ing XP prac­tices. Con­trib­u­tors to the method­ol­o­gy’s devel­op­ment include Ward Cun­ning­ham, Mar­tin Fowler, and others.
Unlike oth­er agile method­olo­gies, XP is exclu­sive­ly used in soft­ware devel­op­ment. It can­not be applied to oth­er busi­ness­es or dai­ly life like Scrum, Kan­ban, or Lean. 
The goal of XP is to cope with con­stant­ly chang­ing require­ments for the soft­ware prod­uct and to enhance devel­op­ment qual­i­ty. There­fore, XP is suit­able for com­plex and uncer­tain projects.

XP revolves around four core activ­i­ties: cod­ing, test­ing, design­ing, and lis­ten­ing. Addi­tion­al­ly, Extreme Pro­gram­ming has core val­ues: sim­plic­i­ty, com­mu­ni­ca­tion, feed­back, courage, and respect.

13 Prac­tices of Extreme Programming

1. The Whole Team

All project par­tic­i­pants using XP work as a sin­gle team. This team must include a cus­tomer rep­re­sen­ta­tive, prefer­ably a real end-user knowl­edge­able about the busi­ness. The cus­tomer sets the prod­uct require­ments and pri­or­i­tizes func­tion­al­i­ty. Busi­ness ana­lysts can assist the cus­tomer. From the execu­tors’ side, the team includes devel­op­ers, testers, some­times a coach guid­ing the team, and a man­ag­er pro­vid­ing resources.

2. Plan­ning Game

Plan­ning in XP occurs in two stages: release plan­ning and iter­a­tion planning.
  • Release Plan­ning: The pro­gram­ming team meets with the cus­tomer to deter­mine the desired func­tion­al­i­ty for the next release, typ­i­cal­ly in 2 – 6 months. Since cus­tomer require­ments are often vague, devel­op­ers clar­i­fy and break them down into tasks that can be com­plet­ed in a day or less. The cus­tomer must under­stand the oper­a­tional envi­ron­ment where the prod­uct will work.

    Tasks are record­ed on cards, and the cus­tomer pri­or­i­tizes them. Devel­op­ers then esti­mate the time required for each task. Once tasks are described and esti­mat­ed, the cus­tomer reviews the doc­u­men­ta­tion and approves the start of work. For project suc­cess, it is crit­i­cal that the cus­tomer and the pro­gram­ming team play on the same field: the cus­tomer choos­es gen­uine­ly nec­es­sary func­tion­al­i­ty with­in the bud­get, and pro­gram­mers appro­pri­ate­ly align the cus­tomer’s require­ments with their capabilities.
  • Iter­a­tion Plan­ning: Con­duct­ed every two weeks, some­times more or less fre­quent­ly. The cus­tomer is present to define the func­tion­al­i­ty for the next iter­a­tion and make changes to the prod­uct requirements.

3. Small Releases

XP releas­es are fre­quent but with lim­it­ed func­tion­al­i­ty. This approach makes it eas­i­er to test and main­tain the sys­tem’s oper­abil­i­ty and pro­vides the cus­tomer with busi­ness-val­ue func­tion­al­i­ty every iteration.

4. Cus­tomer Tests

The cus­tomer spec­i­fies auto­mat­ed accep­tance tests to check the func­tion­al­i­ty of the prod­uct. The team writes these tests and uses them to test the code.

5. Col­lec­tive Code Ownership

In XP, any devel­op­er can mod­i­fy any part of the code, as the code does not belong to its author but to the entire team.

6. Con­tin­u­ous Integration

New code parts are inte­grat­ed into the sys­tem imme­di­ate­ly — XP teams release a new build every few hours or more fre­quent­ly. This prac­tice ensures that recent changes’ impact on the sys­tem is vis­i­ble imme­di­ate­ly. If a new piece of code breaks some­thing, iden­ti­fy­ing and fix­ing the error is much easier.

7. Cod­ing Standards

With col­lec­tive code own­er­ship, adopt­ing com­mon cod­ing stan­dards is cru­cial to make the code look like it was writ­ten by a sin­gle pro­fes­sion­al. Teams can devel­op their stan­dards or adopt exist­ing ones.

8. Sys­tem Metaphor

The sys­tem metaphor is a com­par­i­son with some­thing famil­iar to cre­ate a shared vision with­in the team. Typ­i­cal­ly, the per­son devel­op­ing the archi­tec­ture and see­ing the sys­tem as a whole devis­es the metaphor.

9. Sus­tain­able Pace

XP teams work at max­i­mum pro­duc­tiv­i­ty while main­tain­ing a sus­tain­able pace. Extreme Pro­gram­ming dis­cour­ages over­time and pro­motes a 40-hour work week.

10. Test-Dri­ven Devel­op­ment (TDD)

One of the most chal­leng­ing prac­tices in XP. Pro­gram­mers write tests before writ­ing the code to be test­ed. This approach ensures that each func­tion­al­i­ty piece is ful­ly cov­ered by tests. When devel­op­ers com­mit code, unit tests are run imme­di­ate­ly, and all tests must pass, ensur­ing the team is mov­ing in the right direction.

11. Pair Programming

Imag­ine two devel­op­ers work­ing at one com­put­er on a sin­gle func­tion­al­i­ty piece. This prac­tice is pair pro­gram­ming, the most con­tro­ver­sial prac­tice in XP. The say­ing two heads are bet­ter than one” illus­trates its essence well. From two solu­tions to a prob­lem, the best one is cho­sen, code is opti­mized imme­di­ate­ly, and errors are caught before they occur, result­ing in clean code under­stood by both developers.

12. Sim­ple Design

Sim­ple design in XP means doing only what is need­ed now, with­out try­ing to pre­dict future func­tion­al­i­ty. Sim­ple design and con­tin­u­ous refac­tor­ing cre­ate a syn­er­gis­tic effect — when the code is sim­ple, it is eas­i­er to optimize.

13. Refac­tor­ing

Refac­tor­ing is the ongo­ing process of improv­ing the sys­tem’s design to meet new require­ments. It includes remov­ing code dupli­ca­tion, increas­ing cohe­sion, and reduc­ing cou­pling. XP man­dates con­stant refac­tor­ing, so the code design always remains simple.

Advan­tages and Dis­ad­van­tages of XP

XP is con­tro­ver­sial and often crit­i­cized by those who failed to imple­ment it. How­ev­er, its ben­e­fits are appar­ent when the team ful­ly uti­lizes at least one XP practice. 

The ben­e­fits of striv­ing for XP include:

  • Cus­tomer Sat­is­fac­tion: Cus­tomers get the prod­uct they need, even if they don’t ini­tial­ly have a clear vision.
  • Flex­i­bil­i­ty: The team quick­ly makes code changes and adds new func­tion­al­i­ty due to sim­ple code design, fre­quent plan­ning, and releases.
  • Reli­a­bil­i­ty: Code always works due to con­stant test­ing and con­tin­u­ous integration.
  • Main­tain­abil­i­ty: The team can eas­i­ly main­tain the code because it is writ­ten to a sin­gle stan­dard and con­stant­ly refactored.
  • Pro­duc­tiv­i­ty: Rapid devel­op­ment pace due to pair pro­gram­ming, no over­time, and cus­tomer involvement.
  • High-Qual­i­ty Code
  • Risk Mit­i­ga­tion: Devel­op­ment risks are reduced as respon­si­bil­i­ty is even­ly dis­trib­uted, and the project is not jeop­ar­dized by the depar­ture or arrival of team members.
  • Cost Effi­cien­cy: Devel­op­ment costs are low­er as the team focus­es on code rather than doc­u­men­ta­tion and meetings.

Despite its advan­tages, XP does not always work and has sev­er­al weaknesses:

  • Cus­tomer Involve­ment: Suc­cess depends on cus­tomer involve­ment, which can be chal­leng­ing to achieve.
  • Unpre­dictable Time­lines: It is dif­fi­cult to pre­dict project time costs as the full list of require­ments is unknown at the start.
  • Depen­den­cy on Skill Lev­el: XP heav­i­ly depends on the pro­gram­mers’ skill lev­el and works best with senior professionals.
  • Man­age­ment Resis­tance: Man­age­ment often oppos­es pair pro­gram­ming, ques­tion­ing the need to pay two pro­gram­mers instead of one.
  • Cost: Fre­quent meet­ings with pro­gram­mers can be expen­sive for customers.
  • Cul­tur­al Changes: Imple­ment­ing XP requires sig­nif­i­cant cul­tur­al changes.
  • Lack of Struc­ture: XP’s lack of struc­ture and doc­u­men­ta­tion makes it unsuit­able for large projects.
  • Non-func­tion­al Require­ments: Func­tion­al require­ments are chal­leng­ing to describe as user sto­ries in agile methodologies.

Prin­ci­ples of XP

In his first book, Kent Beck out­lined the fol­low­ing prin­ci­ples of XP: sim­plic­i­ty, com­mu­ni­ca­tion, feed­back, and courage. In a sub­se­quent edi­tion, he added a fifth prin­ci­ple — respect.

1. Sim­plic­i­ty

XP devel­op­ment starts with the sim­plest solu­tion that meets the cur­rent func­tion­al need. Team mem­bers con­sid­er only what needs to be done now and do not incor­po­rate func­tion­al­i­ty that might be need­ed in the future.

2. Com­mu­ni­ca­tion

Com­mu­ni­ca­tion in XP occurs live rather than through doc­u­men­ta­tion. The team active­ly com­mu­ni­cates with each oth­er and the customer.

3. Feed­back

Feed­back in XP is imple­ment­ed in three ways:
  1. Sys­tem Feed­back: Through con­stant mod­ule testing.
  2. Cus­tomer Feed­back: The cus­tomer is part of the team and par­tic­i­pates in writ­ing accep­tance tests.
  3. Team Feed­back: Dur­ing plan­ning, con­cern­ing devel­op­ment time estimates.

4. Courage

Some XP prac­tices are so uncon­ven­tion­al that they require courage and con­stant self-control.

5. Respect

Respect in XP means respect­ing the team and self-respect. Team mem­bers should not make changes that break the com­pi­la­tion, mod­ule tests, or slow down col­leagues’ work. Each mem­ber strives for the high­est code and design quality.

Imple­ment­ing XP and the Workflow

Kent Beck rec­om­mends imple­ment­ing XP to solve project issues. The team selects the most urgent prob­lem and solves it using one of the XP prac­tices. Then, they move on to the next prob­lem, using anoth­er prac­tice. This approach ensures that prob­lems moti­vate XP adop­tion, and the team grad­u­al­ly mas­ters all method­ol­o­gy tools.

To imple­ment XP in an exist­ing project, grad­u­al­ly adopt its prac­tices in the fol­low­ing areas:

  • Test­ing: The team cre­ates tests before writ­ing new code and grad­u­al­ly refac­tors old code.
  • Design: The team con­tin­u­ous­ly refac­tors old code, typ­i­cal­ly before adding new functionality.
  • Plan­ning: The team must close­ly inter­act with the customer.
  • Man­age­ment: Man­agers ensure all team mem­bers fol­low the new rules.
  • Devel­op­ment: Start by orga­niz­ing work­sta­tions for pair pro­gram­ming and encour­age pairs to pro­gram most of the time.

Exam­ple of a Work­flow Using XP

Who Uses XP

Accord­ing to a 2016 Ver­sionOne sur­vey, only 1% of agile com­pa­nies use XP in its pure form. Anoth­er 10% use a hybrid of Scrum and XP.
While XP is not the most com­mon method­ol­o­gy, its prac­tices are used by most com­pa­nies employ­ing agile method­olo­gies. For instance, Piv­otal Soft­ware, Inc. attrib­ut­es its suc­cess to XP.

Piv­otal Soft­ware, Inc.

Piv­otal Soft­ware, Inc. devel­ops busi­ness ana­lyt­ics based on big data and pro­vides con­sult­ing ser­vices. Their prod­ucts are used by cor­po­ra­tions like Ford, Mer­cedes, BMW, GAP, Humana, major banks, gov­ern­ment agen­cies, and insur­ance companies.

Piv­otal advo­cates agile method­olo­gies as essen­tial for mod­ern devel­op­ment. Among the agile vari­ants, they chose XP, a win-win approach for cus­tomers and pro­gram­ming teams. Their work­day starts with stand-up meet­ings and ends at 6:00 PM — no over­time. Piv­otal uses plan­ning games, pair pro­gram­ming, con­stant test­ing, con­tin­u­ous inte­gra­tion, and oth­er XP practices.

What to Read to Under­stand XP

  1. Extreme Pro­gram­ming Explained,” Plan­ning Extreme Pro­gram­ming,” Test-Dri­ven Devel­op­ment” by Kent Beck: These books by the cre­ator of XP pro­vide an in-depth under­stand­ing of the method­ol­o­gy and its advantages.
  2. Refac­tor­ing: Improv­ing the Design of Exist­ing Code” by Mar­tin Fowler: A book by an XP co-author explain­ing the prin­ci­ples and tech­niques of refactoring.
  3. Extreme Pro­gram­ming Applied: Play­ing to Win” by Ken Auer and Roy Miller: A prac­ti­cal guide to XP prac­tices with examples.

Tools for Imple­ment­ing XP in Teams

Red­mine

A free, open-source task man­ag­er with fea­tures like mul­ti­ple project sup­port, flex­i­ble task man­age­ment, Gantt charts, time track­ing, doc­u­men­ta­tion man­age­ment, and task cre­ation via email.

Base­camp


A sim­ple, user-friend­ly ser­vice for col­lab­o­ra­tive project work, includ­ing a task man­ag­er, mes­sage boards, built-in chat, file stor­age, and calendar.

Jira


A robust ser­vice designed for agile project devel­op­ers, com­bin­ing a bug track­er and project man­age­ment tool with many fea­tures and syn­chro­niza­tion options.

Work­sec­tion


A secure ser­vice for project work, allow­ing task set­ting and process con­trol, cor­re­spon­dence track­ing, fil­ter cus­tomiza­tion, time and finan­cial track­ing, and file management.

Con­clu­sion

Extreme Pro­gram­ming is an agile method­ol­o­gy focused on pro­duc­ing high-qual­i­ty, func­tion­al code with a sim­ple archi­tec­ture. Its pur­pose is to reduce uncer­tain­ty in projects and respond flex­i­bly to chang­ing prod­uct requirements. 

XP is exclu­sive­ly for soft­ware devel­op­ment and can­not be adapt­ed to oth­er businesses. 
It is one of the most chal­leng­ing method­olo­gies to imple­ment due to its thir­teen prac­tices. How­ev­er, its prac­tices are wide­ly used in agile projects, prov­ing their effectiveness.

The authors advise grad­u­al­ly mas­ter­ing XP prac­tices while solv­ing project issues. If you see the ben­e­fits, con­tin­ue in the same spir­it. There is no oblig­a­tion to imple­ment XP on an all-or-noth­ing basis. After all, agile method­olo­gies should be flex­i­ble in appli­ca­tion — adapt­ing to the needs of the spe­cif­ic project team.

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