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Chapter 3

Software Engineering

 Agile Development

Software Engineering: A Practitioner’s Approach

by Roger S. Pressman

Software Engineering
By Ian Sommerville
 The Manifesto for 2
Agile Software Development
“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.”
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What is “Agility”?

 Effective (rapid and adaptive) response to change

 Effective communication among all stakeholders
 Drawing the customer onto the team
 Organizing a team so that it is in control of the work performed
Yielding …
 Rapid, incremental delivery of software
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Agility and the Cost of Change
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An Agile Process

 Is driven by customer descriptions of what is required (scenarios)

 Recognizes that plans are short-lived
 Develops software iteratively with a heavy emphasis on construction activities
 Delivers multiple ‘software increments’
 Adapts as changes occur
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Agility Principles - I

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.
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Agility Principles - II

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.
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Human Factors

 The process molds to the needs of the people and team, not the other way
around
 key traits must exist among the people on an agile team and the team itself:
 Competence.
 Common focus.
 Collaboration.
 Decision-making ability.
 Fuzzy problem-solving ability.
 Mutual trust and respect.
 Self-organization.
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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 velocity” is used to help define subsequent
delivery dates for other increments
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Extreme Programming (XP)

 XP Design
 Follows the KIS(Keep It Simple) principle
 For difficult design problems, suggests the creation of “spike
solutions”—a design prototype
 Encourages “refactoring”—an iterative refinement of the internal
program design
 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
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Extreme Programming (XP)

spike solut ions

simple design
prot ot ypes
CRC cards
user st ories
values
accept ance t est crit eria
it erat ion plan

refact oring

pair
programming

Release
sof t ware increment
unit t est
project velocit y comput ed cont inuous int egrat ion

accept ance t est ing

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Adaptive Software Development

 Originally proposed by Jim Highsmith.

 A technique for building complex software and systems.
 ASD focus on human collaboration and team self-organization.
 Team members must trust each other.
 Constructive criticism
 ASD life cycle consists of three phases
 Speculation
 Collaboration
 Learning
 Adaptive Software Development

 Speculation
 Mission statement.
 Project constraints (e.g., delivery dates or user descriptions).
 Basic requirements—to define the set of release cycles (software increments) that will be required for the project.
 Collaboration
 Criticize without animosity.
 Assist without resentment.
 Work as hard as or harder than they do.
 Have the skill set to contribute to the work at hand.
 Communicate problems or concerns in a way that leads to effective action.

 Learning
 Technical reviews
 Project postmortems.
Adaptive Software Development

 ASD — distinguishing features

 Mission-driven planning
 Component-based focus
 Uses “time-boxing” (time-boxing is a constraint used by teams to help focus on
value. Time-boxing refers to the act of putting strict time boundaries around an
action or activity. )
 Explicit consideration of risks
 Emphasizes collaboration for requirements gathering
 Emphasizes “learning” throughout the process
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Adaptive Software Development
Dynamic Systems Development Method

 The Dynamic Systems Development Method (DSDM) is an agile software

development approach that “provides a framework for building and
maintaining systems which meet tight time constraints through the use of
incremental prototyping in a controlled project environment”.
 The DSDM philosophy is borrowed from a modified version of the Pareto
principle—80 percent of an application can be delivered in
20 percent of the time it would take to deliver the complete (100 percent)
application.
Dynamic Systems Development
Method

 DSDM life cycle that defines three different iterative cycles, preceded by
two additional life cycle activities:
Feasibility study—establishes the basic business requirements and
constraints associated with the application to be built
Business study—establishes the functional and information requirements
Functional model iteration—produces a set of incremental prototypes that
demonstrate functionality for the customer.
Design and build iteration—revisits prototypes built during functional model
iteration
Implementation—places the latest software increment
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Dynamic Systems Development Method

 DSDM—distinguishing features
 Similar in most respects to XP and/or ASD
 Nine guiding principles
 Active user involvement is imperative.
 DSDM teams must be empowered to make decisions.
 The focus is on frequent delivery of products.
 Fitness for business purpose is the essential criterion for acceptance of deliverables.
 Iterative and incremental development is necessary to converge on an accurate business solution.
 All changes during development are reversible.
 Requirements are baselined at a high level
 Testing is integrated throughout the life-cycle.
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Dynamic Systems Development Method
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Scrum

 Originally proposed by Schwaber and Beedle

 Scrum—distinguishing features
 Development work is partitioned into “packets”
 Testing and documentation are on-going as the product is constructed
 Work occurs in “sprints” and is derived from a “backlog” of existing requirements
(sprint- time boxed iteration in development)
 Meetings are very short and sometimes conducted without chairs
 “demos” are delivered to the customer with the time-box allocated
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Scrum
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Crystal

 Proposed by Cockburn and Highsmith

 Crystal—distinguishing features
 Actually a family of process models that allow
“maneuverability” based on problem characteristics
 Face-to-face communication is emphasized
 Suggests the use of “reflection workshops” to review the
work habits of the team
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Feature Driven Development

 Originally proposed by Peter Coad et al

 FDD—distinguishing features
 Emphasis is on defining “features”
 a feature “is a client-valued function that can be implemented in
two weeks or less.”
 Uses a feature template
 <action> the <result> <by | for | of | to> a(n) <object>
 A features list is created and “plan by feature” is conducted
 Design and construction merge in FDD
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Feature Driven Development
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Agile Modeling

 Originally proposed by Scott Ambler

 Suggests a set of agile modeling principles
 Model with a purpose
 Use multiple models
 Travel light
 Content is more important than representation
 Know the models and the tools you use to create them
 Adapt locally