Software Engineering | Extreme Programming (XP)

Extreme programming (XP) is one of the most important software development frameworks of Agile models. It is used to improve software quality and responsiveness to customer requirements. The extreme programming model recommends taking the best practices that have worked well in the past in program development projects to extreme levels. 

Good practices need to be practiced in extreme programming: Some of the good practices that have been recognized in the extreme programming model and suggested to maximize their use are given below:

• Code Review: Code review detects and corrects errors efficiently. It suggests pair programming as coding and reviewing of written code carried out by a pair of programmers who switch their works between them every hour.
• Testing: Testing code helps to remove errors and improves its reliability. XP suggests test-driven development (TDD) to continually write and execute test cases. In the TDD approach, test cases are written even before any code is written.
• Incremental development: Incremental development is very good because customer feedback is gained and based on this development team comes up with new increments every few days after each iteration.
• Simplicity: Simplicity makes it easier to develop good quality code as well as to test and debug it.
• Design: Good quality design is important to develop good quality software. So, everybody should design daily.
• Integration testing: It helps to identify bugs at the interfaces of different functionalities. Extreme programming suggests that the developers should achieve continuous integration by building and performing integration testing several times a day.

Basic principles of Extreme programming: XP is based on the frequent iteration through which the developers implement User Stories. User stories are simple and informal statements of the customer about the functionalities needed. A User Story is a conventional description by the user of a feature of the required system. It does not mention finer details such as the different scenarios that can occur. Based on User stories, the project team proposes Metaphors. Metaphors are a common vision of how the system would work. The development team may decide to build a Spike for some features. A Spike is a very simple program that is constructed to explore the suitability of a solution being proposed. It can be considered similar to a prototype. Some of the basic activities that are followed during software development by using the XP model are given below:

• Coding: The concept of coding which is used in the XP model is slightly different from traditional coding. Here, the coding activity includes drawing diagrams (modeling) that will be transformed into code, scripting a web-based system, and choosing among several alternative solutions.
• Testing: XP model gives high importance to testing and considers it to be the primary factor to develop fault-free software.
• Listening: The developers need to carefully listen to the customers if they have to develop good quality software. Sometimes programmers may not have the depth knowledge of the system to be developed. So, the programmers should understand properly the functionality of the system and they have to listen to the customers.
• Designing: Without a proper design, a system implementation becomes too complex and very difficult to understand the solution, thus making maintenance expensive. A good design results elimination of complex dependencies within a system. So, effective use of suitable design is emphasized.
• Feedback: One of the most important aspects of the XP model is to gain feedback to understand the exact customer needs. Frequent contact with the customer makes the development effective.
• Simplicity: The main principle of the XP model is to develop a simple system that will work efficiently in the present time, rather than trying to build something that would take time and may never be used. It focuses on some specific features that are immediately needed, rather than engaging time and effort on speculations of future requirements.
• Pair Programming: XP encourages pair programming where two developers work together at the same workstation. This approach helps in knowledge sharing, reduces errors and improves code quality.
• Continuous Integration: In XP, developers integrate their code into a shared repository several times a day. This helps to detect and resolve integration issues early on in the development process.
• Refactoring: XP encourages refactoring, which is the process of restructuring existing code to make it more efficient and maintainable. Refactoring helps to keep the codebase clean, organized and easy to understand.
• Collective Code Ownership: In XP, there is no individual ownership of code. Instead, the entire team is responsible for the codebase. This approach ensures that all team members have a sense of ownership and responsibility towards the code.
• Planning Game: XP follows a planning game, where the customer and the development team collaborate to prioritize and plan development tasks. This approach helps to ensure that the team is working on the most important features and delivers value to the customer.
• On-site Customer: XP requires an on-site customer who works closely with the development team throughout the project. This approach helps to ensure that the customer’s needs are understood and met, and also facilitates communication and feedback.

Applications of Extreme Programming (XP): Some of the projects that are suitable to develop using the XP model are given below:

• Small projects: XP model is very useful in small projects consisting of small teams as face-to-face meeting is easier to achieve.
• Projects involving new technology or Research projects: This type of project face changing requirements rapidly and technical problems. So XP model is used to complete this type of project.
• Web development projects: XP model is well-suited for web development projects as the development process is iterative and requires frequent testing to ensure the system meets the requirements.
• Collaborative projects: XP model is useful for collaborative projects that require close collaboration between the development team and the customer.
• Projects with tight deadlines: XP model can be used in projects that have a tight deadline, as it emphasizes simplicity and iterative development.
• Projects with rapidly changing requirements: XP model is designed to handle rapidly changing requirements, making it suitable for projects where requirements may change frequently.
• Projects where quality is a high priority: XP model places a strong emphasis on testing and quality assurance, making it a suitable approach for projects where quality is a high priority.

Extreme Programming (XP) is an Agile software development methodology that focuses on delivering high-quality software through frequent and continuous feedback, collaboration, and adaptation. XP emphasizes a close working relationship between the development team, the customer, and stakeholders, with an emphasis on rapid, iterative development and deployment.

Agile development approaches evolved in the 1990s as a reaction to documentation and bureaucracy based processes, particularly the waterfall approach. Agile approaches are based on some common principles, some of which are:

1. Working software is the key measure of progress in a project.
2. For progress in a project, therefore software should be developed and delivered rapidly in small increments.
3. Even late changes in the requirements should be entertained.
4. Face-to-face communication is preferred over documentation.
5. Continuous feedback and involvement of customer is necessary for developing good-quality software.
6. Simple design which envolves and improves with time is a better approach than doing an elaborate design up front for handling all possible scenarios.
7. The delivery dates are decided by empowered teams of talented individuals.

Extreme programming is one of the most popular and well-known approaches in the family of agile methods. an XP project starts with user stories which are short description of what scenarios the customers and users would like the system to support. Each story is written on a separate card, so they can be flexibly grouped.

XP, and other agile methods, are suitable for situations where the volume and space of requirements change is high and where requirement reisks are considerable.

XP includes the following practices:

1. Continuous Integration: Code is integrated and tested frequently, with all changes reviewed by the development team.
2. Test-Driven Development: Tests are written before code is written, and the code is developed to pass those tests.
3. Pair Programming: Developers work together in pairs to write code and review each other’s work.
4. Continuous Feedback: Feedback is obtained from customers and stakeholders through frequent demonstrations of working software.
5. Simplicity: XP prioritizes simplicity in design and implementation, with the goal of reducing complexity and improving maintainability.
6. Collective Ownership: All team members are responsible for the code, and anyone can make changes to any part of the codebase.
7. Coding Standards: Coding standards are established and followed to ensure consistency and maintainability of the code.
8. Sustainable Pace: The pace of work is maintained at a sustainable level, with regular breaks and opportunities for rest and rejuvenation.
9. XP is well-suited to projects with rapidly changing requirements, as it emphasizes flexibility and adaptability. It is also well-suited to projects with tight timelines, as it emphasizes rapid development and deployment.
10. Refactoring: Code is regularly refactored to improve its design and maintainability, without changing its functionality.
11. Small Releases: Software is released in small increments, allowing for frequent feedback and adjustments based on that feedback.
12. Customer Involvement: Customers are actively involved in the development process, providing feedback and clarifying requirements.
13. On-Site Customer: A representative from the customer’s organization is present with the development team to provide continuous feedback and answer questions.
14. Short Iterations: Work is broken down into short iterations, usually one to two weeks in length, to allow for rapid development and frequent feedback.
15. Planning Game: The team and customer work together to plan and prioritize the work for each iteration, with the goal of delivering the most valuable features first.
16. Metaphor: A shared metaphor is used to guide the design and implementation of the system.
17. Coding Standards: Coding standards are established and followed to ensure consistency and maintainability of the code.

Advantages of Extreme Programming (XP):

• Slipped schedules − Timely delivery is ensured through slipping timetables and doable development cycles.
• Misunderstanding the business and/or domain − Constant contact and explanations are ensured by including the client on the team.
• Canceled projects − Focusing on ongoing customer engagement guarantees open communication with the consumer and prompt problem-solving.
• Staff turnover − Teamwork that is focused on cooperation provides excitement and goodwill. Team spirit is fostered by multidisciplinary cohesion.
• Costs incurred in changes − Extensive and continuing testing ensures that the modifications do not impair the functioning of the system. A functioning system always guarantees that there is enough time to accommodate changes without impairing ongoing operations.
• Business changes − Changes are accepted at any moment since they are seen to be inevitable.
• Production and post-delivery defects: Emphasis is on − the unit tests to find and repair bugs as soon as possible.