Chapter 3 Agile Software Development
Agile development techniques
Agile project management
Scaling agile methods
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 radi
ally reduce the delivery time for working software systems"
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
Plan-driven and agile 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.
Specification, design, implementation and testing are inter-leaved and the outputs from the developme
t process are decided through a process of negotiation during the software development process."
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 qu
ckly to changing requirements without excessive rework."
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 toolsWorking 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.
The principles of agile methods
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.
Agile development techniques
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.
The extreme programming release cycle
Extreme programming practices (a) , Extreme programming practices (b), XP and agile principles, "Incremental development is supported through small, frequent system releases.
Customer involvement means full-time customer engagement with the team.
People not process through pair programming, collective ownership and a process that avoids long working hours.
Change supported through regular system releases.
Maintaining simplicity through constant refactoring of
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.
User stories for specification
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.
A prescribing medication story
Examples of task cards for prescribing medication , Refactoring, "Conventional wisdom in software engineering is to design for change. It is worth spending time and effort anticipating changes as this reduces costs later in the life cycle.
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.
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.
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.
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:
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.
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.
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.
However, people adopting the customer role have limited time available and so cannot work full-time with the development team. They may feel that providing
he requirements was enough of a contribution and so may be reluctant to get involved in the testing process. "
Test case description for dose checking
Test automation, "Test automation means that tests are written as executable components before the task is implemented
These testing components should be stand-alone, should simulate the submission of input to be tested and should check that the result meets the output specification. An automated test framework (e.g. Junit) is a system that makes it easy to write executable tests and submit a set of tests for execution.
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.
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 is difficult to judge the comple
eness of a set of tests. Although you may have a lot of system tests
your test set may not provide complete coverage.
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.
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 effic
ent than 2 programmers working separately. "
Agile project management
Agile project management
The principal responsibility of software project managers is to manage the project so that the software is delivered on time and within the planned budget for the project.
The standard approach to project management is plan-driven. Managers draw up a plan for the project showing what should be delivered, when it should be delivered and who will work on the development of the project deliverables.
Agile project management requires a different approach, which is adapte
to incremental development and the practices used in agile methods. "
Scrum is an agile method that focuses on managing iterative development rather than specific agile practices.
There are three phases in Scrum.
The initial phase is an outline planning phase where you establish the general objectives for the project and design the software architecture.
This is followed by a series of sprint cycles, where each cycle develops an increment of the system.
The project closure phase wraps up the project, completes required documentation such as system help
rames and user manuals and assesses the lessons learned from the project. "
Scrum terminology (a)