eXtreme Programming Angelo Corsaro (modified by G. Blank, with notes from Extreme Programming FAQ and Mike Rogers, BrainLoaf.com)corsaro@cs.wustl.eduhttp://tao.doc.wustl.edu/~corsaro

Table of ContentsSoftware Development Life Cycle (SWDLC).SWDLC Models.Cost Of Change.XP Introduction.XPs Values.XPs Principles.XPs Practices.Putting it all Together.An XP Project Road-Map.References.

A Brief OverviewA Software Development Life Cycle (SWDLC) is an abstract representation of how software is developed.A SWDLC process can consist ofSequential Phases/StepsParallel Phases/StepsThe Phases of a SWDLC process are typicallyRequirement AnalysisDesign SpecificationCoding and Unit TestingTest and IntegrationAcceptance TestSystem and Software MaintenanceSoftware Development Life Cycle

Generic Waterfall ModelAssume a development process in which the step 1-6 outlined before are executed one after the other in sequential order.SWDLC ModelsRequirementsDesignCodingUnit TestingTest IntegrationAcceptance TestMaintenance

Generic Waterfall ModelThis model in not practical, it fails in capturing the inherent iterative nature of SW development.SW development has concurrent and iterative aspects that this model fail to capture.Does not encourage prototyping and software reuse.The DOD SWDLC uses a variation of the Waterfall-Model.NASA uses a SWDLC development model that is a minor variation of the DOD SWDLC.SWDLC Models

Risk: The Basic ProblemThe basic problem of SW development is risk.Sample of risks areSchedule slipsProject CancelledSystem Goes SourDefect RateBusiness MisunderstoodFalse Feature-RichStaff TurnoverCommonly used SWDLC fall short in coping with the previously cited risks.SWDLC Models

Spiral Model 1/2Is a Risk-Driven approach to SW development.It encompass both the best features of both classic life cycles and prototyping.PlanningRisk AnalysisPrototypingClient EvaluationAnd InputDevelopmentPrototypingSWDLC ModelsReq AnalysisDesign Spec.Test and Integration.Coding Unit TestingAccptance Test

Spiral Model 2/2The Spiral Model can be used effectively for bothSystem EnhancementSystem DevelopmentMost SWDLC can be considered as a special case of the Spiral Model.The embedded Risk-Analysis built into the model avoids many of the difficulties that arise in other models.SWDLC Models

Cost of ChangeOne Universal Assumption of SW Engineering is that the cost of changing a program rises exponentially over timeOne of the key assumption of XP is that the cost of changing a program, can be kept mostly constant over time. This assumption is based on real-world experience, and on the use of both betterProgramming Practice Programming EnvironmentsThis assumption about the cost of change gives the opportunity of taking a totally different approach to SW development.

Extreme Programming (XP)XP does not involve bungee cords! And it predates Windows XP.Developed by Kent Beck (also developed CRC cards)A light-weight methodology for small to medium-sized teams developing software in the face of vague or rapidly changing requirements -- Kent Beck"Extreme Programming turns the conventional software process sideways. Rather than planning, analyzing, and designing for the far-flung future, XP programmers do all of these activities a little at a time throughout development. IEEE Computer October 1999 XP Introduction

Main XP ConceptsXP is a lightweight development processInstead of lots of documentation nailing down what the customer wants up front, emphasize continuous communication and feedback between developers and programmersEmbrace change: iterate often, design and redesign, code and test frequently, keep the customer involved.Deliver software to the customer in short (2 week) iterationsSeeks to eliminate defects early, thus reducing costs

XP is made of a collection ofValuesRules/PrinciplesPracticesIn XP values, principles and practices are often set to the extreme level, from here the name eXtreme ProgrammingXP Introduction

The Four Core Values of XPCommunication.Simplicity.Feedback.Courage.XP Values

CommunicationOften problem that arise in SW project can be tracked back to lack of communication.XP enforces the Communication Value by employing many practice that could not be carried without communicating (e.g. pair programming, unit testing etc.).XP employs a Coach whose job is that of noticing when people are not communicating and reintroduce them.XP Values

Simplicity''Do the simplest thing that could possibly work'' (DTSTTCPW) principle (elsewhere known as KISS).An XP coach may say DTSTTCPW when he sees an XP developer doing something that is needlessly complicated. YAGNI principle (''You aint gonna need it'')Simplicity and Communication support each other mutually.XP Values

FeedbackFeedback works in XP at different time scales.Programmers have feedback on a minutes time scale on the status of the system thanks to unit tests.When customers write new stories the programmers estimate those immediately to give prompt feedback to the customer about the quality of the stories.The customer review the scheduler every 2-3 weeks and provide prompt feedback to the developer.XP Values

CourageXP team should have the courage of throwing code away.XP team should have the courage of mainly refactor the architecture of the system, if architectural flaw are detected.Courage has in XP the same role that mutation has in genetic algorithms. Takes you out of local maximum/minimum.

XP Values

Core XP PrinciplesRapid Feedback.Assume Simplicity.Incremental Change.Embracing the Change.Quality Work.XP Principles

Twelve XP PracticesThe Planning Game.Small Releases.Metaphor.Simple Design.Testing.Refactoring.Pair Programming.Collective Ownership.Continuous Integration.40-Hours a Week.On-Site Customer.Coding Standards.

XP Practices

XP Practices (1)The Planning Game.Customer and developers cooperate to produce the maximum business value as rapidly as possible. Customer comes up with a list of desired features for the system.Each feature is written out as a User Story, giving each feature a name and describes in broad strokes what is required. User stories are typically written in 2-3 sentences on 4x6 story cards.Developers estimate how much effort each story will take, and how much effort the team can produce in a given time interval (iteration). Project velocity = how many days can be committed to project per week.Customer decides which stories to implement in what order, and when and how often to produce a production releases of the system.

XP Practices

XP Practices (2-4)Small releases.Start with the smallest useful feature set. Release early and often, adding a few features each time. Releases can be date driven or user story driven.System metaphor.Each project has an organizing metaphor, which provides an easy to remember naming convention. Simple design.Always use the simplest possible design that gets the job done. The requirements will change tomorrow, so only do what's needed to meet today's requirements (remember, YAGNI).XP Practices

XP Practices (5)Continuous TestingBefore programmers add a feature, they write a test for it. When the suite runs, the job is done. Tests in XP come in two basic flavors. Unit Tests automate testing of functionality as developers write it.Each unit test typically tests only a single class, or a small cluster of classes. Unit tests typically use a unit testing framework, such as JUnit. Acceptance Tests (or Functional Tests) are specified by the customer to test that the overall system is functioning as specified.When all the acceptance tests pass for a given user story, that story is considered complete. Could consist of a script of user interface actions and expected results that a human can run. Ideally acceptance tests should be automated, either using the unit testing framework, or a separate acceptance testing framework. XP Practices

XP Practices (6)Pair programming.Two programmers work together at one machine.Driver enters code, while navigator critiques it.Periodically switch roles.XP PracticesResearch results:Pair programming increases productivity.Higher quality code in about half the time.Increased satisfaction/decreased frustration).Williams, L., Kessler, R., Cunningham, W., & Jeffries, R. Strengthening the case for pair programming. IEEE Software, 17(3), July/August 2000.Requires proximity in lab or work environment.

XP Practices (7-9)Refactoring.Refactor out any duplicate code generated in a coding session.You can do this with confidence that you didn't break anything because you have the tests. Collective code ownership.No single person "owns" a module. Any developer can work on any part of the code base at any time. Continuous integration.All changes are integrated into the codebase at least daily. Tests have to run 100% both before and after integration.XP Practices

XP Practices (10-12)

40-hour work week.Programmers go home on time. In crunch mode, up to one week of overtime is allowed. More than that and theres something wrong with the process.On-site customer.Development team has continuous access to a real live customer, that is, someone who will actually be using the system, or a proxy. Coding standards.Everyone codes to the same standards. Ideally, you shouldn't be able to tell by looking at it who on the team has touched a specific piece of code. XP Practices

Putting it all TogetherPlanningUser StoriesRelease PlanningRelease PlanMake Frequent Small ReleasesProject VelocityIterative DevelopmentIteration PlanningMove People AroundDaily Stand Up MeetingFix XP When it BreaksDesigningSimplicity is the KeyChoose a System MetaphorCRC CardsSpike SolutionNever add Functionality EarlyRefactor Mercilessly

Daily Standup MeetingGoal: Identify items to be accomplished for the day and raise issues

Everyone attends, including the customer Not a discussion forum Take discussions offline Everyone gets to speak 15 minutes

XP Project

XP Project Iteration

XP Project Development

XP Project Coding

XP vs. Rational Unified Process

ReferencesExtreme Programming Explained, Kent Beck Addison Wesley 1999.http://www.extremeprogramming.orghttp://BrainLoaf.comhttp://Wiki.comhttp://www.xp2001.org