Subject: Software Engineering

Topic: Agile Software Development

Difficulty: High

Extreme Programming (XP) is a pragmatic approach to program development that emphasizes business results first and takes an incremental, get-something-started approach to building the product, using continual testing and revision. XP teams design software for specific purpose without adding any changes that are not specifically requested that may slow down the process, keeping the development course simple through systematic and regular testing and design improvements.

Extreme Programming is based on 12 principles:

The Planning Process - The desired features of the software, which are communicated by the customer, are combined with cost estimates provided by the programmers to determine what the most important factors of the software are. This stage is sometimes called the Planning Game.

Small Releases - The software is developed in small stages that are updated frequently, typically every two weeks.

Metaphor - All members on an XP team use common names and descriptions to guide development and communicate on common terms.

Simple Design - The software should include only the code that is necessary to achieve the desired results communicated by the customer at each stage in the process. The emphasis is not on building for future versions of the product.

Testing - Testing is done consistently throughout the process. Programmers design the tests first and then write the software to fulfill the requirements of the test. The customer also provides acceptance tests at each stage to ensure the desired results are achieved.

Refactoring - XP programmers improve the design of the software through every stage of development instead of waiting until the end of the development and going back to correct flaws.

Pair Programming - All code is written by a pair of programmers working at the same machine.

Collective Ownership - Every line of code belongs to every programmer working on the project, so there are no issues of proprietary authorship to slow the project down. Code is changed when it needs to be changed without delay.

Continuous Integration - The XP team integrates and builds the software system multiple times per day to keep all the programmers at the same stage of the development process at once.