Chapter 3 – Agile Software Development


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Chapter 3 – Agile Software Development
Summary
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Topics covered
• Agile methods • Plan-driven and agile development • Extreme programming • Agile project management • Scaling agile methods
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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.
• 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.
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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.
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Agile manifesto
• 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.
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The principles of agile methods

Principle Customer involvement
Incremental delivery

Description
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.
The software is developed in increments with the customer specifying the requirements to be included in each increment.

People not process Embrace change Maintain simplicity

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.
Expect the system requirements to change and so design the system to accommodate these changes.
Focus on simplicity in both the software being developed and in the development process. Wherever possible, actively work to eliminate complexity from the system.

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Agile method applicability
• Product development where a software company is developing a small or medium-sized product for sale.
• 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 not a lot of external rules and regulations that affect the software.
• Because of their focus on small, tightly-integrated teams, there are problems in scaling agile methods to large systems.
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Problems with agile methods
• It can be difficult to keep the interest of customers who are involved in the process.
• Team members may be unsuited to the intense involvement that characterises agile methods.
• Prioritising changes can be difficult where there are multiple stakeholders.
• Maintaining simplicity requires extra work. • Contracts may be a problem as with other approaches to
iterative development.
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Agile methods and software maintenance
• Most organizations spend more on maintaining existing software than they do on new software development. So, if agile methods are to be successful, they have to support maintenance as well as original development.
• Two key issues:
– Are systems that are developed using an agile approach maintainable, given the emphasis in the development process of minimizing formal documentation?
– Can agile methods be used effectively for evolving a system in response to customer change requests?
• Problems may arise if original development team cannot be maintained.
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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.
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Chapter 3 – Agile Software Development