What is the difference between plan-driven and agile processes?
- Plan-driven processes are processes where all of the process activities are planned in advance and progress is measured against this plan.
- In agile processes, planning is incremental and it is easier to change the process to reflect changing customer requirements.
What are lifecycle models?
Combine the development processes and activities in different ways (different order, once or repeated …) to model the life cycle of a project
•By making models of the life cycle of successful software projects can help us design better approaches to plan the life cycle of future projects
What are the characteristics of rapid software engineering?
Businesses operate in a fast-changing requirement and it is practically impossible to produce a set of stable software requirements
–Specification, design and implementation are interleaved
–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
How to decide on the balance between plan-driven and agile processes?
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.
–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).
–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 system 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 teams.
–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.
–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
–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.
What are agile methods and what o they focus on?
•Dissatisfaction with the overheads involved insoftware design methodsof 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 aimof 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.
What is an 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.
What are principles of agile methods?
- Customer involvement
- Incremental delivery
- People not process
- Embrace change
- Maintain simplicity
When do agile methods apply?
- 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.
What are some problems with agile methods?
- It can be difficult to keep the interest of customers who are involved in the process.
- Team members may be unsuitedto the intense involvement that characterizes agile methods.
- Prioritizing changes can be difficult where there are multiple stakeholders.
- Maintaining simplicity requires extra work.
- Contractsmay be a problem as with other approaches to iterative development.
What are some agile process models?
- Extreme Programming (XP)
- Scrum
- Dynamic Systems Development Method
- Agile Modeling
- Agile Unified Process
What is extreme programming?
•Perhaps the best-known and most widely used agile method. Developed in the late 1990s.
•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.
What are extreme programming principles?
- Incremental planning
- Small releases
- Simple design
- Test-first development
- Refactoring
- Pair programming
- Collective ownership
- Continuous integration
- Sustainable pace
- On-site customer
What is 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.
What is 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 arerun automatically when new functionality is added, thus checking that the new functionality has not introduced errors.
What are problems with test-driven 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.
What is pair programming?
- In pair programming, programmers sit together at the same workstation 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 evidence that a pair working together is more efficient than 2 programmers working separately.
What are the advantages of the 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.
What is scrum?
The Scrum approach is a general agile method but its focus is on managing iterative development rather than specific agile practices.
What are three phases of the scrum?
A.The initial phase is an outline planning phase where you establish the general objectives for the project and design the software architecture.
B.This is followed by a series of sprint cycles, where each cycle develops an increment of the system.
C.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.
What is a sprint?
•Sprints are fixed length, normally 2–4 weeks. They correspond to the development of a release of the system in XP.
What is a sprint cycle?
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.
•Once these are agreed, the team organize themselves to develop the software. During 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 presented to stakeholders. The next sprint cycle then begins.
What does the scrum master do?
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.
What are scrum meetings?
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.
What are 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.
