Bài giảng Introduction to Software Engineering - Week 10: Agile Software Development - Nguyễn Thị Minh Tuyền
Week 10:
Agile Software Development
Nguyễn Thị Minh Tuyền
Adapted from sSlidoemsmoef rIavnille
Topics covered
1. Agile methods
2. Extreme programming
3. Agile project management
4. Scaling agile methods
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Topics covered
1. Agile methods
2. Extreme programming
3. Agile project management
4. Scaling agile methods
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Rapid software development
£ Rapid development and delivery is now often the most
important requirement for software systems
p Businesses operate in a fast – changing requirement and it is
practically impossible to produce a set of stable software
requirements
p Software has to evolve quickly to reflect changing business
needs.
£ Plan-driven development is essential for some types of
system but does not meet these business needs.
£ Agile development methods emerged in the late 1990s
whose aim wdelivery time for
working software systems
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Agile development
£ Program specification, design and implementation are
inter-leaved
£ The system is developed as a series of versions or
increments with stakeholders involved in version
specification and 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
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Plan-driven and agile development
Plan-based development
Design and
implementation
Requirements
engineering
Requirements
specification
Requirements change
requests
Agile development
Requirements
engineering
Design and
implementation
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Plan-driven and agile development
£ Plan-driven development
p A plan-driven approach to software engineering is based around
separate development stages with the outputs to be produced at
each of these stages planned in advance.
p Not necessarily waterfall model – plan-driven, incremental
development is possible
p Iteration occurs within activities.
£ Agile development
p Specification, design, implementation and testing are inter-leaved
and the outputs from the development process are decided through
a process of negotation during the software development process.
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Agile methods
£ Dissatisfaction with the overheads involved in software
design methods of the 1980s and 1990s led to the creation
of agile methods. These methods:
p Focus on the code rather than the design
p Are based on an iterative approach to software development
p Are intended ickly and evolve this
quickly to meet changing requirements.
£ 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.
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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:
p Individuals and interactions over processes and tools
p Working sodocumentation
p Customer collaboration over contract negotiation
p 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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The principles of agile methods
Principle
Description
Customer
involvement
Customers should be closely involved throughout the
development process. Their role is provide and prioritize
new system requirements and to evaluate the iterations of
the system.
Incremental delivery The software is developed in increments with the customer
be included in each
increment.
People not process
The skills of the development team should be recognized
and exploited. Team members should be left to develop
their own ways of working without prescriptive processes.
Embrace change
Maintain simplicity
o change and so design
the system to accommodate these changes.
Focus on simplicity in both the software being developed
and in the development process. Wherever possible,
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actively work to eliminate complexity from the system.
Agile method applicability
£ Product development
p where a software company is developing a small or medium-
sized product for sale.
£ Custom system development within an organization
p where there is a clear commitment from the customer to become
involved iwhere 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.
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Topics covered
1. Agile methods
2. Extreme programming
3. Agile project management
4. Scaling agile methods
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Agile methods
£ Agile Modeling
£ Agile Unified Process (AUP)
£ Dynamic Systems Development Method (DSDM)
£ Essential Unified Process (EssUP)
£ Extreme Programming (XP)
£ Feature Driven Development (FDD)
£ Open Unified Process (OpenUP)
£ Scrum
£ Velocity tracking
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Extreme programming
£ A very influential agile method, developed in the
late 1990s, that introduced a range of agile
development techniques.
£ Extreme Programming (XP) takes an ‘extreme’
approach to iterative development.
p New versions may be built several times per day;
p Increments are delivered to customers every 2 weeks;
p All tests must be run for every build and the build is only
accepted if tests run successfully.
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XP and agile principles
£ Incremental development is supported through small,
frequent system releases.
£ Customer involvement means full-time customer
engagement with the team.
£ People not process through pair programming, collective
ownership and a process that avoids long working hours.
£ Change supported through regular system releases.
£ Maintaining simplicity through constant refactoring of code.
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The extreme programming release cycle
Select user
stories for this
release
Break down
stories to tasks
Plan release
Evaluate
system
Release
software
Develop/integrate/
test software
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Extreme programming practices (a)
Principle or practice Description
Incremental planning Requirements are recorded on story cards and the stories
to be included in a release are determined by the time
available and their relative priority. The developers break
these stories into development ‘Tasks’.
Small releases
The minimal useful set of functionality that provides
business value is developed first. Releases of the system
are frequent and incrementally add functionality to the first
release.
Simple design
Enough design is carried out to meet the current
requirements and no more.
Test-first development An automated unit test framework is used to write tests for
that functionality itself is
implemented.
Refactoring
All developers are expected to refactor the code
continuously as soon as possible code improvements are
found. This keeps the code simple and maintainable.
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Extreme programming practices (b)
Pair programming
Developers work in pairs, checking each other’s work and
providing the support to always do a good job.
Collective ownership The pairs of developers work on all areas of the system,
so that no islands of expertise develop and all the
developers take responsibility for all of the code. Anyone
can change anything.
Continuous
integration
omplete, it is integrated
into the whole system. After any such integration, all the
unit tests in the system must pass.
Sustainable pace
On-site customer
Large amounts of overtime are not considered acceptable
as the net effect is often to reduce code quality and
medium term productivity
the system (the
customer) should be available full time for the use of the
XP team. In an extreme programming process, the
customer is a member of the development team and is
responsible for bringing system requirements to the team
for implementation.
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Influential XP practices
£ Extreme programming has a technical focus and is
not easy to integrate with management practice in
most organizations.
£ Key practices
p User storie
p Refactoring
p Test-first development
p Pair programming
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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 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 e
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