Agile Software Development PDF

Chapter 3 – Agile Software Development Chapter 3 Agile Software 30/10/2014 1 Development Topics covered  Agile methods  Agile development techniques Chapter 3 Agile Software 30/10/2014...

Chapter 3 – Agile Software Development Chapter 3 Agile Software 30/10/2014 1 Development Topics covered  Agile methods  Agile development techniques Chapter 3 Agile Software 30/10/2014 2 Development Rapid software development  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.  Plan-driven development is essential for some types of system but does not meet these business needs.  Agile development methods emerged in the late 1990s whose aim was to radically reduce the delivery time for working software systems Chapter 3 Agile Software 30/10/2014 3 Development Agile development  Program specification, design and implementation are inter-leaved  The system is developed as a series of versions or increments with stakeholders involved in version specification and evaluation  Frequent delivery of new versions for evaluation  Extensive tool support (e.g. automated testing tools) used to support development.  Minimal documentation – focus on working code Chapter 3 Agile Software 30/10/2014 4 Development Plan-driven and agile development Chapter 3 Agile Software 30/10/2014 5 Development Plan-driven and agile development  Plan-driven development  A plan-driven approach to software engineering is based around separate development stages with the outputs to be produced at each of these stages planned in advance.  Not necessarily waterfall model – plan-driven, incremental development is possible  Iteration occurs within activities.  Agile development  Specification, design, implementation and testing are inter- leaved and the outputs from the development process are decided through a process of negotiation during the software development process. Chapter 3 Agile Software 30/10/2014 6 Development  Agile methods Chapter 3 Agile Software 30/10/2014 7 Development Agile methods  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 this 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. Chapter 3 Agile Software 30/10/2014 8 Development The principles of agile methods Principle Description Customer involvement Customers 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 delivery The software is developed in increments with the customer specifying the requirements to be included in each increment. People not process The 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 change Expect the system requirements to change and so design the system to accommodate these changes. Maintain simplicity Focus on simplicity in both the software being developed and in the development process. Wherever possible, actively work to eliminate complexity from the system. Chapter 3 Agile Software 30/10/2014 9 Development Agile method applicability  Product development where a software company is developing a small or medium-sized product for sale.  Virtually all software products and apps are now developed using an agile approach  Custom system development within an organization, where there is a clear commitment from the customer to become involved in the development process and where there are few external rules and regulations that affect the software. Chapter 3 Agile Software 30/10/2014 10 Development  Agile development techniques Chapter 3 Agile Software 30/10/2014 11 Development Extreme programming  A very influential agile method, developed in the late 1990s, that introduced a range of agile development techniques.  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. Chapter 3 Agile Software 30/10/2014 12 Development The extreme programming release cycle Chapter 3 Agile Software 30/10/2014 13 Development Extreme programming practices (a) Principle or practice Description Incremental planning Requirements are recorded on story cards and the stories to be included in a release are determined by the time available and their relative priority. The developers break these stories into development ‘Tasks’. See Figures 3.5 and 3.6. Small releases The minimal useful set of functionality that provides business value is developed first. Releases of the system are frequent and incrementally add functionality to the first release. Simple design Enough design is carried out to meet the current requirements and no more. Test-first development An automated unit test framework is used to write tests for a new piece of functionality before that functionality itself is implemented. Refactoring All developers are expected to refactor the code continuously as soon as possible code improvements are found. This keeps the code simple and maintainable. Chapter 3 Agile Software 30/10/2014 14 Development Extreme programming practices (b) Pair programming Developers work in pairs, checking each other’s work and providing the support to always do a good job. Collective ownership The pairs of developers work on all areas of the system, so that no islands of expertise develop and all the developers take responsibility for all of the code. Anyone can change anything. Continuous integration As soon as the work on a task is complete, it is integrated into the whole system. After any such integration, all the unit tests in the system must pass. Sustainable pace Large amounts of overtime are not considered acceptable as the net effect is often to reduce code quality and medium term productivity On-site customer A representative of the end-user of the system (the customer) should be available full time for the use of the XP team. Chapter 3 Agile Software 30/10/2014 15 Development XP and agile principles  Incremental development is supported through small, frequent system releases.  Customer involvement means full-time customer engagement with the team.  Change supported through regular system releases.  Maintaining simplicity through constant refactoring of code. Chapter 3 Agile Software 30/10/2014 16 Development Influential XP practices  Extreme programming has a technical focus and is not easy to integrate with management practice in most organizations.  Consequently, while agile development uses practices from XP, the method as originally defined is not widely used.  Key practices  User stories for specification  Refactoring  Test-first development  Pair programming Chapter 3 Agile Software 30/10/2014 17 Development User stories for requirements  In XP, a customer or user is part of the XP team and is responsible for making decisions on requirements.  User requirements are expressed as user stories or scenarios.  These are written on cards and the development team break them down into implementation tasks. These tasks are the basis of schedule and cost estimates.  The customer chooses the stories for inclusion in the next release based on their priorities and the schedule estimates. Chapter 3 Agile Software 30/10/2014 18 Development Refactoring  Conventional wisdom in software engineering is to design for change.  XP, however, maintains that this is not worthwhile as changes cannot be reliably anticipated.  Rather, it proposes constant code improvement (refactoring) to make changes easier when they have to be implemented. Chapter 3 Agile Software 30/10/2014 19 Development Refactoring  Programming team look for possible software improvements and make these improvements even where there is no immediate need for them.  This improves the understandability of the software and so reduces the need for documentation.  Changes are easier to make because the code is well- structured and clear.  However, some changes requires architecture refactoring and this is much more expensive. Chapter 3 Agile Software 30/10/2014 20 Development Examples of refactoring  Re-organization of a class hierarchy to remove duplicate code.  Tidying up and renaming attributes and methods to make them easier to understand.  The replacement of inline code with calls to methods that have been included in a program library. Chapter 3 Agile Software 30/10/2014 21 Development Test-first development  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.  Incremental test development from scenarios.  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. Chapter 3 Agile Software 30/10/2014 22 Development Test-driven development  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.  All previous and new tests are run automatically when new functionality is added, thus checking that the new functionality has not introduced errors. Chapter 3 Agile Software 30/10/2014 23 Development Customer involvement  The role of the customer in the testing process is to help develop acceptance tests for the stories that are to be implemented in the next release of the system.  The customer who is part of the team writes tests as development proceeds. All new code is therefore validated to ensure that it is what the customer needs. Chapter 3 Agile Software 30/10/2014 24 Development Test automation  Test automation means that tests are written as executable components before the task is implemented  As testing is automated, there is always a set of tests that can be quickly and easily executed  Whenever any functionality is added to the system, the tests can be run and problems that the new code has introduced can be caught immediately. Chapter 3 Agile Software 30/10/2014 25 Development Problems with test-first development  Programmers prefer programming to testing and sometimes they take short cuts when writing tests. For example, they may write incomplete tests that do not check for all possible exceptions that may occur.  Some tests can be very difficult to write incrementally. For example, in a complex user interface, it is often difficult to write unit tests for the code that implements the ‘display logic’ and workflow between screens.  It difficult to judge the completeness of a set of tests. Although you may have a lot of system tests, your test set may not provide complete coverage. Chapter 3 Agile Software 30/10/2014 26 Development Pair programming  Pair programming involves programmers working in pairs, developing code together.  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 improving the system code. Chapter 3 Agile Software 30/10/2014 27 Development Pair programming  In pair programming, programmers sit together at the same computer 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 some evidence that suggests that a pair working together is more efficient than 2 programmers working separately. Chapter 3 Agile Software 30/10/2014 28 Development Key points  Agile methods are incremental development methods that focus on rapid software development, frequent releases of the software, reducing process overheads by minimizing documentation and producing high-quality code.  Agile development practices include  User stories for system specification  Frequent releases of the software,  Continuous software improvement  Test-first development  Customer participation in the development team. Chapter 3 Agile Software 30/10/2014 29 Development