1. Chapter 3 Agile software development 1 Chapter 3 – Agile Software Development

2. Topics covered Chapter 3 Agile software development 2 Agile Development Extreme Programming (XP) Methodology Pair Programming

3. Rapid software development Chapter 3 Agile software development 3 Rapid development and delivery is now often the most important requirement for software systems  Businesses operate in a fast –changing requirement and it is practically impossible to produce a set of stable software requirements  Software has to evolve quickly to reflect changing business needs. Rapid software development  Specification, design and implementation are inter-leaved  System is developed as a series of versions with stakeholders involved in version evaluation  User interfaces are often developed using an IDE and graphical toolset.

4. What is Agile Development? Chapter 3 Agile software development 4 Agile is an emerging software development methodology Programming-centric  Few rules and practices  Easy to follow Eliminate much of modeling and documentation tasks – saves time Emphasize simple, iterative application development

5. Agile methods Chapter 3 Agile software development 5 Dissatisfaction with the overheads involved in software design methods of the 1980s and 1990s led to the creation of agile methods. These methods:  Focus on the code rather than the design  Are based on an iterative approach to software development  Are intended to deliver working software quickly and evolve quickly to meet changing requirements. The aim of agile methods is to reduce overheads in the software process (e.g. by limiting documentation) and to be able to respond quickly to changing requirements without excessive rework.

6. Agile manifesto Chapter 3 Agile software development 6 We are uncovering better ways of developing software by doing it and helping others do it. Through this work we have come to value:  Individuals and interactions over processes and tools Working software over comprehensive documentation Customer collaboration over contract negotiation Responding to change over following a plan That is, while there is value in the items on the right, we value the items on the left more.

7. The principles of agile methods Chapter 3 Agile software development 7 PrincipleDescription Customer involvementCustomers should be closely involved throughout the development process. Their role is provide and prioritize new system requirements and to evaluate the iterations of the system. Incremental deliveryThe software is developed in increments with the customer specifying the requirements to be included in each increment. People not processThe skills of the development team should be recognized and exploited. Team members should be left to develop their own ways of working without prescriptive processes. Embrace changeExpect the system requirements to change and so design the system to accommodate these changes. Maintain simplicityFocus on simplicity in both the software being developed and in the development process. Wherever possible, actively work to eliminate complexity from the system.

8. Extreme Programming Chapter 3 Agile software development 8 Perhaps the best-known and most widely used agile method. Extreme Programming (XP) takes an ‘extreme’ approach to iterative development.  New versions may be built several times per day;  Increments are delivered to customers every 2 weeks;  All tests must be run for every build and the build is only accepted if tests run successfully.

9. Extreme Programming (cont.) Chapter 3 Agile software development 9 Extreme Programming is founded on four core values:  Communication  Simplicity  Feedback  Courage Developers must provide rapid feedback to the end users on a continuous basis XP requires developers to follow the KISS principle

10. Extreme Programming (cont.) Chapter 3 Agile software development 10 Developers must make incremental changes to grow the system – must embrace change Developers must have a quality first mentality Three key principles used by XP to create successful systems:  Continuous testing  Coding performed by pairs of developers  Close interactions with end users

11. Extreme Programming (cont.) Chapter 3 Agile software development 11 XP project begins with user stories that describe what the system needs to do Programmers code in small, simple modules and test to meet those needs Users are required to be available to clear up questions and issues Standards are very important to minimize confusion XP projects deliver results sooner than even the RAD approaches

12. Problems with XP Chapter 3 Agile software development 12 For large projects, applying XP is not easy XP is only recommended for small groups of developers—no more than 10 developers Project members need to work well and co-operate as part of a team XP requires a great deal of discipline – otherwise projects will become unfocused and chaotic Maintaining large systems built with XP is difficult – lack of analysis and design documentation, only code documentation On-site customer availability not always possible

13. Testing in XP Chapter 3 Agile software development 13 Testing is central to XP and XP has developed an approach where the program is tested after every change has been made. XP testing features:  Test-first development.  User involvement in test development and validation.  Automated test harnesses are used to run all component tests each time that a new release is built.

14. Test-first development Chapter 3 Agile software development 14 Writing tests before code clarifies the requirements to be implemented. Tests are written as programs rather than data so that they can be executed automatically. The test includes a check that it has executed correctly.  Usually relies on a testing framework such as Junit. All previous and new tests are run automatically when new functionality is added, thus checking that the new functionality has not introduced errors.

15. Pair programming Chapter 3 Agile software development 15 In XP, programmers work in pairs, sitting together to develop code. This helps develop common ownership of code and spreads knowledge across the team. It serves as an informal review process as each line of code is looked at by more than 1 person. It encourages refactoring as the whole team can benefit from this. Measurements suggest that development productivity with pair programming is similar to that of two people working independently.

16. Pair programming (cont.) Chapter 3 Agile software development 16 In pair programming, programmers sit together at the same workstation to develop the software. Pairs are created dynamically so that all team members work with each other during the development process. The sharing of knowledge that happens during pair programming is very important as it reduces the overall risks to a project when team members leave. Pair programming is not necessarily inefficient and there is evidence that a pair working together is more efficient than 2 programmers working separately.

17. Advantages of pair programming Chapter 3 Agile software development 17 It supports the idea of collective ownership and responsibility for the system.  Individuals are not held responsible for problems with the code. Instead, the team has collective responsibility for resolving these problems. It acts as an informal review process because each line of code is looked at by at least two people. It helps support refactoring, which is a process of software improvement.  Where pair programming and collective ownership are used, others benefit immediately from the refactoring so they are likely to support the process.

18. References Cornell University, USA http://www.cs.cornell.edu/courses/cs501/2000fa/slides.html Picture collect from: Ivan Marsic, Rutgers University Ian Sommerville, Software Engineering, 9 th edition, Pearson, 2011 Roger s. pressman, Software Engineering a practitioners approach, 7 th ed

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