Agile Methods
Steven J Zeil:
Abstract
Agile methods are a modern variant of incremental development.
They emphasze:
- Iterative & incremental development
- Frequent communication with customer representatives
- Short “time-boxed” development cycles
- Focus on quality as a matter of professional pride
This lesson is a discussion of the origins of Agile Development and a quick overview of the basic principles.
1 Agile as a Social Entity
1.1 Agile Development is
- A reaction against heavily-managed, documentation-heavy processes
- A social movement within the software development profession
- Introduced in the Agile Manifesto (2001)
1.1.1 The 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.
1.1.2 The Twelve Principles of Agile Software
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.
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.
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.
1.2 Variations
- Extreme programming
- Scrum
2 Common Practices of Agile Development
source: The Agile Alliance
2.1 Fundamentals
2.1.1 Teams
- small groups, largely full-time
- contains all required skills (technical and domain expertise)
- Stakeholder representative(s) is a regular team member
2.1.2 Iterative development
- Activities repeat (analysis, design, testing, …)
- Work products can be revisited (enhancements, refactoring, etc.)
- Scheduling may focus on short, repeated development cycles
2.1.3 Incremental development
- Each successive version of the product
- is “usable”
- adds user-visible functionality
- Contrast this with a strategy of delivering successive, complete subsystems that will not be revisited
- Think of building a house by adding room after room, as opposed to pouring the whole foundation, then framing all the exterior walls, then laying all the floors, then doing all the electrical wiring, then doing all the plumbing, then…
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When can you start using the house?
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2.1.4 Version Control
- ’nuff said
2.2 Common Intersections
2.2.1 Iteration Planning
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Teams typically try for 4-10 stories per iteration
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Select stories to implement in current implementation
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Often organized onto a task board
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Velocity
Rate at which functionality (user stories) completed per iteration.
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Most agile approaches define a fixed number of days per iteration
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Add up the effort estimates of all stories completed during an iteration. This is the team’s current velocity.
- Used to estimate time remaining to complete the project
Task Board
Contains stories to be completed in current iteration
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Combines story cards and task notes
- task notes indicate team member responsible
- color coding may designate feature, bug, general notes
- each task is marked with an estimate of hours required
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Task notes organized in columns
- To do: tasks yet to be started
- In process: task that team members are working on
- To verify: believed completed, needs to be checked
- Done: verified as completed. Some boards also list
- Backlog: related stories not being handled this iteration
2.2.2 Sustainable pace
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Setting a work pace that can be sustained indefinitely
- overtime only in critical, unusual, and limited circumstances
- Some evidence shows that routine overtime reduces productivity
- overtime only in critical, unusual, and limited circumstances
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Once a pace has been established, teams can measure velocity
2.2.3 Meetings
- Emphasis on co-location of teams to enhance communication
- Daily meetings to review key coordination points
- \first-term{time-boxed} to very short time periods (e.g., 15 min.)
- Any topic that starts a discussion is cut short and discussed by interested parties after the meeting
- Three Questions (Scrum)
- What have you completed since the last meeting?
- What do you plan to complete by the next meeting?
- What is getting in your way?
- Avoid “Yesterday I did X. Today I will continue working on X”
- the Scrum Zombie pattern
- helps if user stories define units of work that can be completed in a day
2.2.4 Rules of Simplicity
(Kent Beck)
Each code unit
- is verified by automated tests
- contains no duplication
- expresses separately each distinct idea or responsibility
- contains the minimum number of components compatible with the first 3 rules
2.2.5 TDD
Test-Driven Development goes beyond our previously-cited “test first, code later” rule
- write a “single” unit test describing an unimplemented functionality
- run the test (it should fail at this stage)
- write “just enough” code to make the test pass
- refactor the code until it conforms to the rules of simplicity
The four steps above are repeated, adding new, tested functionality each time.
2.2.6 Simple Design
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Design is on-going
Principles include
- refactoring
- YAGNI
“You Ain’t Gonna Need It” - argument against early design of elaborate components for future use: “We going to need X eventually. We might was well design it now.” “YAGNI”
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Design should be emergent
- good global design will emerge from careful attention to local design questions
- Wishful thinking?
- good global design will emerge from careful attention to local design questions
2.2.7 Familiar Intersections
- Refactoring
- Continuous Integration