1、Agile Software Development,Agile methods Plan-driven and agile development Extreme programming (XP) Agile project management Pair Programming Scrum Scaling agile methods,1,Rapid software development,Rapid development and delivery is now often the most important requirement for software systems Busin
2、esses 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 a
3、s a series of versions with stakeholders involved in version evaluation User interfaces are often developed using an IDE and graphical toolset.,2,Agile methods,Dissatisfaction with the overheads involved in software design methods of the 1980s and 1990s led to the creation of agile methods. These me
4、thods: 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
5、 documentation) and to be able to respond quickly to changing requirements without excessive rework.,3,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 t
6、ools 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.,4,The principles of agile methods,5,Agile method applicabil
7、ity,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
8、 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.,6,Problems with agile methods,It can be difficult to keep the interest of customers who are involved in the process. Team members may be
9、 unsuited to the intense involvement that characterizes agile methods. Prioritizing 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.,7,Agile methods and software m
10、aintenance,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 main
11、tainable, 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.,8,Plan-driven and agile development,P
12、lan-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 activ
13、ities. 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.,9,Plan-driven and agile specification,10,Technical, human, organizational iss
14、ues,Most projects include elements of plan-driven and agile processes. Deciding on the balance depends on: Is it important to have a very detailed specification and design before moving to implementation? If so, you probably need to use a plan-driven approach. Is an incremental delivery strategy, wh
15、ere you deliver the software to customers and get rapid feedback from them, realistic? If so, consider using agile methods. How large is the system that is being developed? Agile methods are most effective when the system can be developed with a small co-located team who can communicate informally.
16、This may not be possible for large systems that require larger development teams so a plan-driven approach may have to be used.,11,Technical, human, organizational issues,What type of system is being developed? Plan-driven approaches may be required for systems that require a lot of analysis before
17、implementation (e.g. real-time system with complex timing requirements). What is the expected system lifetime? Long-lifetime systems may require more design documentation to communicate the original intentions of the system developers to the support team. What technologies are available to support s
18、ystem development? Agile methods rely on good tools to keep track of an evolving design How is the development team organized? If the development team is distributed or if part of the development is being outsourced, then you may need to develop design documents to communicate across the development
19、 teams.,12,Extreme programming,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
20、build and the build is only accepted if tests run successfully.,13,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 own
21、ership and a process that avoids long working hours. Change supported through regular system releases. Maintaining simplicity through constant refactoring of code.,14,The extreme programming release cycle,15,Extreme programming practices (a),16,Extreme programming practices (b),17,Requirements scena
22、rios,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 scenarios or user stories. These are written on cards and the development team break them down into implementation tasks. These tasks are the basis of sch
23、edule and cost estimates. The customer chooses the stories for inclusion in the next release based on their priorities and the schedule estimates.,18,XP and change,Conventional wisdom in software engineering is to design for change. It is worth spending time and effort anticipating changes as this r
24、educes 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.,19,Refactoring,Programming team look for possible s
25、oftware 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 arc
26、hitecture refactoring and this is much more expensive.,20,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 inclu
27、ded in a program library.,21,Testing in XP,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 valida
28、tion. Automated test harnesses are used to run all component tests each time that a new release is built.,22,Test-first 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. The t
29、est 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.,23,Customer involvement,The role of the cust
30、omer 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. H
31、owever, people adopting the customer role have limited time available and so cannot work full-time with the development team. They may feel that providing the requirements was enough of a contribution and so may be reluctant to get involved in the testing process.,24,Test automation,Test automation
32、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 sys
33、tem 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 introdu
34、ced can be caught immediately.,25,XP testing difficulties,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 wr
35、ite 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
36、 not provide complete coverage.,26,Pair programming,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.
37、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.,27,Pair programming,In pair programming, programmers sit together at the same workstation to develop the
38、 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 necessa
39、rily inefficient and there is evidence that a pair working together is more efficient than 2 programmers working separately.,28,Advantages of pair programming,It supports the idea of collective ownership and responsibility for the system. Individuals are not held responsible for problems with the co
40、de. 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 owner
41、ship are used, others benefit immediately from the refactoring so they are likely to support the process.,29,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 pro
42、ject. 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 a
43、dapted to incremental development and the particular strengths of agile methods.,30,Scrum,The Scrum approach is a general agile method but its focus is on managing iterative development rather than specific agile practices. There are three phases in Scrum. The initial phase is an outline planning ph
44、ase 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 he
45、lp frames and user manuals and assesses the lessons learned from the project.,31,The Scrum process,32,The Sprint cycle,Sprints are fixed length, normally 24 weeks. They correspond to the development of a release of the system in XP. The starting point for planning is the product backlog, which is th
46、e list of work to be done on the project. The selection phase involves all of the project team who work with the customer to select the features and functionality to be developed during the sprint.,33,The Sprint cycle,Once these are agreed, the team organize themselves to develop the software. Durin
47、g this stage the team is isolated from the customer and the organization, with all communications channelled through the so-called Scrum master. The role of the Scrum master is to protect the development team from external distractions. At the end of the sprint, the work done is reviewed and present
48、ed to stakeholders. The next sprint cycle then begins.,34,Teamwork in Scrum,The Scrum master is a facilitator who arranges daily meetings, tracks the backlog of work to be done, records decisions, measures progress against the backlog and communicates with customers and management outside of the tea
49、m. The whole team attends short daily meetings where all team members share information, describe their progress since the last meeting, problems that have arisen and what is planned for the following day. This means that everyone on the team knows what is going on and, if problems arise, can re-pla
50、n short-term work to cope with them.,35,Scrum benefits,The product is broken down into a set of manageable and understandable chunks. Unstable requirements do not hold up progress. The whole team have visibility of everything and consequently team communication is improved. Customers see on-time delivery of increments and gain feedback on how the product works. Trust between customers and developers is established and a positive culture is created in which everyone expects the project to succeed.,
