Agile Software Development
Rapid software development focusPlan-driven and agile development
- Specification, design and implementation are inter- leaved - System is developed as a series of versions with stakeholders involved in version 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
agile manifesto
1.individuals and interactions over processes and tools 2. Working software over comprehensive documentation 3. Customer collaboration over contract negotiation 4.Responding to change over following a plan
Agility Principles (Agile Alliance) 5-8
5. Build projects around motivated individuals. Give them the environment and support they need, and trust them to get the job done. 6. The most efficient and effective method of conveying information to and within a development team is face-to-face conversation. 7. Working software is the primary measure of progress. 8. Agile processes promote sustainable development. The sponsors, developers, and users should be able to maintain a constant pace indefinitely.
Agility Principles (Agile Alliance)9-12
9. Continuous attention to technical excellence and good design enhances agility. 10.Simplicity - the art of maximizing the amount of work not done - is essential. 11.The best architectures, requirements, and designs emerge from self-organizing teams. 12.At regular intervals, the team reflects on how to become more effective, then tunes and adjusts its behavior accordingly.
Scaling out
is concerned with how agile methods can be introduced across a large organization with many years of software development experience.
Working software ...
over comprehensive documentation
Customer collaboration ...
over contract negotiation
Responding to change...
over following a plan
Individuals and interactions...
over processes and tools
Plan-driven development
plan based development -> requirements engineering -> requirements specification -> design and implement -> requirements change requests
agile development
requirements engineering -> design and implementation -> repeat
extreme programming release cycle
select user stories for release -> break down stories to tasks -> plan release -> develop/integrate/test software -> release -> evaluate
why pair program
• 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
Scrum
• Originally proposed by Schwaber and Beedle • The Scrum approach is a general agile method but its focus is on managing iterative development rather than specific agile practices.
what type of system is being developed?
• Plan-driven approaches may be required for systems that require a lot of analysis before implementation (e.g. real-time system with complex timing requirements).
Agile method applicability
• Product development where a software company is developing a small or medium-sized product for sale. • Customsystemdevelopmentwithinan 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.
XP Coding
- Recommends the construction of a UNIT TEST for a store before coding commences - Encourages "PAIR PROGRAMMING"
XP Testing
- All unit tests are executed DAILY - "ACCEPTANCE TESTS" are defined by the customer and executed to assess customer visible functionality
XP Design
- Follows the KIS PRINCIPLE - Encourage the use of CRC cards (see Chapter 8) - For difficult design problems, suggests the creation of "SPIKE SOLUTIONS"—a design prototype - Encourages "REFACTORING"—an iterative refinement of the internal program design
XP and agile principles
- incremental development through small, frequent releases - customer involvement - people not process through pair programming, collective ownership - change through regular system release - keep simplicity through constant refactoring
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.
Extreme programming practices
1. Incremental planning 2. Small releases 3. Simple design 4. Test-first development 5. Refactoring 6. Pair programming 7. Collective ownership 8. Continuous integration 9. Sustainable pace 10. On-site customer
Agility Principles (Agile Alliance) 1-4
1. Our highest priority is to satisfy the customer through early and continuous delivery of valuable software. 2. Welcome changing requirements, even late in development. Agile processes harness change for the customer's competitive advantage. 3. Deliver working software frequently, from a couple of weeks to a couple of months, with a preference to the shorter timescale. 4. Business people and developers must work together daily throughout the project.
Scrum phases
A. Outline planning B. Series of sprint cycles C. Project closure phase
Extreme Programming (XP)
Developed in the late 1990s. • 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.
scaling out and scaling up agile
Scaling up, scaling out When scaling agile methods it is important to maintain agile fundamentals - Flexible planning, frequent system releases, continuous integration, test-driven development and good team communications.
outline planning phase
The initial phase is an outline planning phase where you establish the general objectives for the project and design the software architecture.
Project closure phase
The project closure phase wraps up the project, completes required documentation such as system help frames and user manuals and assesses the lessons learned from the project.
Series of sprint cycles
each cycle develops an increment of the system.
'brownfield systems
include and interact with a number of existing systems. Many of the system requirements are concerned with this interaction and so don't really lend themselves to flexibility and incremental development.
Scrum master
the team is isolated from the customer and the organization, with all communications channelled through the 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 presented to stakeholders. The next sprint cycle then begins.
Technical, human, organizational issues
what type of system is being developed? What is the expected system lifetime? How is the development team organized? What technologies are available to support system development?
Scaling up
• 'Scaling up' is concerned with using agile methods for developing large software systems that cannot be developed by a small team.
Scaling agile methods
• Agile methods have proved to be successful for small and medium sized projects that can be developed by a small co-located team. • It is sometimes argued that the success of these methods comes because of improved communications which is possible when everyone is working together. • Scaling up agile methods involves changing these to cope with larger, longer projects where there are multiple development teams, perhaps working in different locations.
What technologies are available to support system development?
• Agile methods rely on good tools to keep track of an evolving design
XP and change: 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.
the principles of agile methods
• Customer involvement • Incremental delivery • People not process • Embrace change • Maintain simplicity
Scrum terminology
• Development team • Potentially shippable product increment • Product backlog • Product owner • Scrum • ScrumMaster • Sprint • Velocity
Agile methods: creation and 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.
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
Scaling up to large systems
• For large systems development, it is not possible to focus only on the code of the system. You need to do more up- front design and system documentation • Cross-team communication mechanisms have to be designed and used. This should involve regular phone and video conferences between team members and frequent, short electronic meetings where teams update each other on progress. • Continuous integration, where the whole system is built every time any developer checks in a change, is practically impossible. However, it is essential to maintain frequent system builds and regular releases of the system.
Is the system subject to external regulation?
• If a system has to be approved by an external regulator (e.g. the FAA approve software that is critical to the operation of an aircraft) then you will probably be required to produce detailed documentation as part of the system safety case.
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 teams.
Requirements scenarios
• 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 schedule and cost estimates. • The customer chooses the stories for inclusion in the next release based on their priorities and the schedule estimates.
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.
How good are the designers and programmers in the development team?
• It is sometimes argued that agile methods require higher skill levels than plan-based approaches in which programmers simply translate a detailed design into code
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 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.
Agile maintenance
• Key problems are: - Lack of product documentation - Keeping customers involved in the development process - Maintaining the continuity of the development team • Agile development relies on the development team knowing and understanding what has to be done. • For long-lifetime systems, this is a real problem as the original developers will not always work on the system.
Large system development 2
• Large systems and their development processes are often constrained by external rules and regulations limiting the way that they can be developed. • Large systems have a long procurement and development time. It is difficult to maintain coherent teams who know about the system over that period as, inevitably, people move on to other jobs and projects. • Large systems usually have a diverse set of stakeholders. It is practically impossible to involve all of these different stakeholders in the development process.
Large systems development
• Large systems are usually collections of separate, communicating systems, where separate teams develop each system. Frequently, these teams are working in different places, sometimes in different time zones. • Large systems are 'brownfield systems', that is they include and interact with a number of existing systems. Many of the system requirements are concerned with this interaction and so don't really lend themselves to flexibility and incremental development. • Where several systems are integrated to create a system, a significant fraction of the development is concerned with system configuration rather than original code development.
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.
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.
Agile and plan-driven methods
• 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, where 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. This may not be possible for large systems that require larger development teams so a plan- driven approach may have to be used.
Contractual issues
• Most software contracts for custom systems are based around a specification, which sets out what has to be implemented by the system developer for the system customer. • However, this precludes interleaving specification and development as is the norm in agile development. • A contract that pays for developer time rather than functionality is required. - However, this is seen as a high risk my many legal departments because what has to be delivered cannot be guaranteed.
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.
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.
Scaling out to large companies
• Project managers who do not have experience of agile methods may be reluctant to accept the risk of a new approach. • Large organizations often have quality procedures and standards that all projects are expected to follow and, because of their bureaucratic nature, these are likely to be incompatible with agile methods. • Agile methods seem to work best when team members have a relatively high skill level. However, within large organizations, there are likely to be a wide range of skills and abilities. • There may be cultural resistance to agile methods, especially in those organizations that have a long history of using conventional systems engineering processes.
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.
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.
The Scrum sprint cycle
• Sprints are fixed length, normally 2-4 weeks. • The starting point for planning is the product backlog, which is the 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 from the product backlog to be developed during the sprint.
The Sprint cycle
• Sprints are fixed length, normally 2-4 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 the 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.
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.
Testing in XP: 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.
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 team. • 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-plan short-term work to cope with them.
Practical problems with agile methods
• The informality of agile development is incompatible with the legal approach to contract definition that is commonly used in large companies. • Agile methods are most appropriate for new software development rather than software maintenance. Yet the majority of software costs in large companies come from maintaining their existing software systems. • Agile methods are designed for small co-located teams yet much software development now involves worldwide distributed teams.
Extreme Programming (XP)
• The most widely used agile process, originally proposed by Kent Beck • XP Planning - Begins with the creation of "USER STORIES" - Agile team assesses each story and assigns a COST - Stories are grouped to for a DELIVERABLE INCREMENT - A COMMITMENT is made on delivery date - After the first increment "PROJECT VELCOCITY" is used to help define subsequent delivery dates for other increments
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 adapted to incremental development and the particular strengths of agile methods.
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.
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. • 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 the requirements was enough of a contribution and so may be reluctant to get involved in the testing process.
Pair programming
• This helps develop common ownership of code and spreads knowledge across the team. • informal review process, each LOC is looked at by >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.
Are there cultural or organizational issues that may affect the system development?
• Traditional engineering organizations have a culture of plan- based development, as this is the norm in engineering.
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 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.
