Extreme Programming Extreme Programming XP Formulated in 1999

Extreme Programming

Extreme Programming (XP) ü Formulated in 1999 by Kent Beck, Ward Cunningham and Ron Jeffries ü Agile software development methodology (others: Scrum, DSDM) ü Developed in reaction to high ceremony methodologies

XP: Why? ü Previously: ü Get all the requirements before starting design ü Freeze the requirements before starting development ü Resist changes: they will lengthen schedule ü Build a change control process to ensure that proposed changes are looked at carefully and no change is made without intense scrutiny ü Deliver a product that is obsolete on release

XP: Embrace Change ü Recognize that: ü All requirements will not be known at the beginning ü Requirements will change ü Use tools to accommodate change as a natural process ü Do the simplest thing that could possibly work and refactor mercilessly ü Emphasize values and principles rather than process

XP Practices (Source: http: //www. xprogramming. com/xpmag/whatisxp. htm)

XP Practices: Whole Team ü All contributors to an XP project are one team ü Must include a business representative--the ‘Customer’ ü Provides requirements ü Sets priorities ü Steers project ü Team members are programmers, testers, analysts, coach, manager ü Best XP teams have no specialists

XP Practices: Planning Game ü Two key questions in software development: ü Predict what will be accomplished by the due date ü Determine what to do next ü Need is to steer the project ü Exact prediction (which is difficult) is not necessary

XP Practices: Planning Game ü XP Release Planning ü Customer presents required features ü Programmers estimate difficulty ü Imprecise but revised regularly ü XP Iteration Planning ü ü ü Two week iterations Customer presents features required Programmers break features down into tasks Team members sign up for tasks Running software at end of each iteration

XP Practices: Customer Tests ü The Customer defines one or more automated acceptance tests for a feature ü Team builds these tests to verify that a feature is implemented correctly ü Once the test runs, the team ensures that it keeps running correctly thereafter ü System always improves, never backslides

XP Practices: Small Releases ü Team releases running, tested software every iteration ü Releases are small and functional ü The Customer can evaluate or in turn, release to end users, and provide feedback ü Important thing is that the software is visible and given to the Customer at the end of every iteration

XP Practices: Simple Design ü Build software to a simple design ü Through programmer testing and design improvement, keep the software simple and the design suited to current functionality ü Not a one-time thing nor an up-front thing ü Design steps in release planning and iteration planning ü Teams design and revise design through refactoring, through the course of the project

XP Practices: Pair Programming ü All production software is built by two programmers, sitting side by side, at the same machine ü All production code is therefore reviewed by at least one other programmer ü Research into pair programming shows that pairing produces better code in the same time as programmers working singly ü Pairing also communicates knowledge throughout the team

XP Practices: Test-Driven Development ü Teams practice TDD by working in short cycles of adding a test, and then making it work ü Easy to produce code with 100 percent test coverage ü These programmer tests or unit tests are all collected together ü Each time a pair releases code to the repository, every test must run correctly

XP Practices: Design Improvement ü Continuous design improvement process called ‘refactoring’: ü Removal of duplication ü Increase cohesion ü Reduce coupling ü Refactoring is supported by comprehensive testing--customer tests and programmer tests

XP Practices: Continuous Integration ü Teams keep the system fully integrated at all times ü Daily, or multiple times a day builds ü Avoid ‘integration hell’ ü Avoid code freezes

XP Practices: Collective Code Ownership ü Any pair of programmers can improve any code at any time ü No ‘secure workspaces’ ü All code gets the benefit of many people’s attention ü Avoid duplication ü Programmer tests catch mistakes ü Pair with expert when working on unfamiliar code

XP Practices: Coding Standard ü Use common coding standard ü All code in the system must look as though written by an individual ü Code must look familiar, to support collective code ownership

XP Practices: Metaphor ü XP Teams develop a common vision of the system ü With or without imagery, define common system of names ü Ensure everyone understands how the system works, where to look for functionality, or where to add functionality

XP Practices: Sustainable Pace ü Team will produce high quality product when not overly exerted ü Avoid overtime, maintain 40 hour weeks ü ‘Death march’ projects are unproductive and do not produce quality software ü Work at a pace that can be sustained indefinitely

XP Values ü Communication ü Simplicity ü Feedback ü Courage

XP Values: Communication ü Poor communication in software teams is one of the root causes of failure of a project ü Stress on good communication between all stakeholders--customers, team members, project managers ü Customer representative always on site ü Paired programming

XP Values: Simplicity ü ‘Do the Simplest Thing That Could Possibly Work’ ü Implement a new capability in the simplest possible way ü Refactor the system to be the simplest possible code with the current feature set ü ‘You Aren’t Going to Need It’ ü Never implement a feature you don’t need now

XP Values: Feedback ü Always a running system that delivers information about itself in a reliable way ü The system and the code provides feedback on the state of development ü Catalyst for change and an indicator of progress

XP Values: Courage ü Projects are people-centric ü Creativity of people and not any process that causes a project to succeed

XP Criticism ü Unrealistic--programmer centric, not business focused ü Detailed specifications are not written ü Design after testing ü Constant refactoring ü Customer availability ü practices are too interdependent

XP Thoughts ü The best design is the code. ü Testing is good. Write tests before code. Code is complete when it passes tests. ü Simple code is better. Write only code that is needed. Reduce complexity and duplication. ü Keep code simple. Refactor. ü Keep iterations short. Constant feedback.