BTS530: Major Project
Planning and Design
Iterative Development
References:
Agile
& Iterative Development, by Craig Larman, 2004, Addison
Wesley.
Applying UML and Patterns, 3rd Edition, Chapter 21, Craig Larman
Web sites as listed
Agenda
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Iterative development
Agile modeling
SCRUM
Extreme Programming
Refactoring
Iterative Development
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Product development lifecycle is composed of
several iterations in sequence, each delivering a
“chunk” of functionality
Each iteration is a self-contained mini project:
Planning
 Development (including testing)
 Implementation
 Review/Refactoring
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Iterative Development
Initial Requirements, Vision
+ Feedback/Input from Iterations
Iteration
1
Iteration
2
Iteration
3
Production System
(grows with each iteration)
…
(Typically
between 3
and 30
iterations in a
system
development
project)
Iterative Development
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Each Iteration
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Plan
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tasks, time estimates, milestones
Track/Control progress
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adjust scope if required
Develop
 Implement
 Review/Refactor
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Iterative Development
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Planning Each Iteration
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Risk driven
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Client driven
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choose riskiest, most difficult elements
choose highest business value
Ideally—a mixture of both
Iterative Development
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Tracking/Controlling
Timeframes for iterations are typically shorter than
for traditionally run projects, necessitating more
control
 “Timeboxing” Approach is common in iterative
development methodologies using agile methods

Iterations typically 1 to 6 weeks
 Scope adjusted if necessary; not time, not quality

Iterative Development
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Benefits over “Big Bang” approaches
“Depth” vs “breadth” – issues through to
implementation uncovered and addressed more
quickly
 Early results reveal and enable required changes—
end product is more suitable
 Early results enable more accurate estimates for the
rest of the system
 Momentum sustained…constant visible progress
 Other?
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Agile Methods
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Iterative methods typically (but not always)
employ agile methods
Agile methods defined and supported by
http://www.agilealliance.org/
Agile methods start with the “Manifesto for
Agile Software Development”
http://www.agilemanifesto.org
Agile Methods
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Principles
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http://www.agilemanifesto.org/principles.html
Agile Methods
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Iterative development methodologies employing
agile methods include:
Scrum
 Extreme Programming (XP)
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SCRUM: Intro
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An agile method for software development.
Projects progress via a series of iterations called
sprints.
Each sprint iteration is approx. 2-4 weeks long.
Ideally suited to projects with rapidly changing
or “sudden” requirements.
Mountain Goat Software http://www.mountaingoatsoftware.com/scrum
SCRUM: the players
Product Owner
Key
Stakeholder
or user
Scrum Master
Ensures team
productivity by
removing roadblocks
and protecting the team
from the “outside”
Scrum Team
--5-9 people
--no traditional roles
--All working together
Mountain Goat Software http://www.mountaingoatsoftware.com/scrum
SCRUM
Product Backlog: a prioritized list of features containing every
desired feature or change to the product. Prioritized by the
product owner.
Mountain Goat Software http://www.mountaingoatsoftware.com/scrum
SCRUM
A Sprint Planning Meeting is held at the start of each sprint. The
product owner reprioritizes the product backlog and the scrum team
decides what it can complete in the coming Sprint. The result is the
Sprint Backlog a list of tasks to complete all work in the current sprint.
Mountain Goat Software http://www.mountaingoatsoftware.com/scrum
SCRUM
The Scrum: a daily meeting for entire Scrum team: Scrum
Master asks “What did you do yesterday?”; “What will you do
today?”; “Are there any roadblocks?”
Mountain Goat Software http://www.mountaingoatsoftware.com/scrum
SCRUM
At the end of a sprint the team has a Sprint
Review Meeting to demonstrate the result
of the sprint: a Product Increment.
Scrum
Product
Backlog
Sprint
Backlog
2-4 Week
Sprint
Product
Increment
(working, highquality software)
Mountain Goat Software http://www.mountaingoatsoftware.com/scrum
XP: Intro
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A form of agile software development.
Promotes simplicity and agility
Managers, customers, developers are equal
partners in the development team
http://www.extremeprogramming.org
XP: Specifications
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User Stories are at the heart of XP
They are written by the customers, are each
about 2-3 sentences long and are similar to
scenarios.
User stories drive acceptance tests
User stories are the “specs”
http://www.extremeprogramming.org
XP: Iterations
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A Release Planning Meeting creates a release
plan which details which user stories will go into
a release (80 + or – 20 is the “norm”)
An Iteration Planning Meeting is held at the
start of each Iteration in the release to decide
what will go into that iteration
Each “time boxed” iteration is usually a constant
length; typically 1-3 weeks.
http://www.extremeprogramming.org
XP: Meetings
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Daily Standup Meeting is used to communicate
problems, solutions, and promote team focus
Everyone stands up in a circle to avoid long
discussions
http://www.extremeprogramming.org
XP: Coding
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Coding done in pairs: Pair Programming
The customer is ALWAYS available
Coding Standards must be followed
Test Driven Development: The Unit Test is
written first
Code is integrated at frequent (hours) intervals
No overtime
Code is Refactored frequently
http://www.extremeprogramming.org
Refactoring: Intro
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Part of each iteration – review and refactor what
is “smelly”
Simplify!
Refactoring
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Structured, disciplined
Rewrite/restructure existing code without
changing its external behaviour
Apply small transformation steps combined with
re-executing test steps
Refactoring
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Why?
remove duplicate code
 improve clarity
 shorten long methods
 remove “hard coded” constraints
 “smelly code” –consider refactoring
 “code stench” – MUST refactor
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Refactoring
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Code Stench
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duplicated code
BIG GIANT METHOD
BIG GIANT CLASS (lots of code)
Class with MANY instance variables
strikingly similar subclasses
little or no use of interfaces in the design
high coupling between many objects
and so on…
Sample Refactorings
Refactoring
Description
Extract Method
transform long method into shorter one by
farming out a portion to a helper method
Extract Constant
replace literal constant with constant variable
Introduce Explaining
Variable
put the result of the expression into a
temporary variable with a name that explains
the purpose
Replace Constructor Call
With Factory Method
For example—in Java, replace using the new
operator and constructor call with invoking a
helper method that creates the object (hiding
the details)
Refactoring
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Examples: pg 391-393, chapter 21, Larman text
Resources
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www.refactoring.com