The Extreme Programming (XP) Model

The
Extreme Programming
Model Damian Gordon
The
Extreme Programming
Model Damian Gordon

Contents
1. Overview
2. Details
3. Advantages
4. Disadvantages
5. Interesting
6. Reflection
7. Review
8. Summary

Overview
• The “Extreme Programming (XP) Model” is a
model that represents one method as to how
software can be developed.

Timeline of Methodologies
6
1950s Code & Fix
1960s Design-Code-Test-Maintain
1970s Waterfall Model
1980s Spiral Model
1990s Rapid Application Development, V Model
2000s Agile Methods

Timeline of Methodologies
7
1950s Code & Fix
1960s Design-Code-Test-Maintain
1970s Waterfall Model
1980s Spiral Model
1990s Rapid Application Development, V Model
2000s Agile Methods

Overview
• Extreme Programming (XP) was created by
Kent Beck during his work on the C3 project.
• Beck became the C3 project leader in 1996
and began to refine the development
methodology used in the project
• He wrote a book on the methodology,
published in October 1999, called Extreme
Programming Explained.
9

Reference
• Beck, K. (1999) “Extreme Programming
Explained: Embrace Change”. Addison-Wesley,
ISBN 978-0321278654.

Kent Beck
• Born in 1961.
• an American software
engineer and the creator
of Extreme Programming
• was one of the 17 original
signatories of the Agile
Manifesto
• the leading proponent of
Test-Driven Development

Extreme Programming (XP)
• The key assumption of XP is:

• The key assumption of XP is:
Embrace Change

• Start with the Planning Game:
• The game is a meeting that occurs once per iteration,
typically once a week. The planning process is
divided into two parts:
– Release Planning: This is focused on determining what
requirements are included in which near-term releases,
and when they should be delivered. The customers and
developers are both part of this.
– Iteration Planning: This plans the activities and tasks of the
developers. In this process the customer is not involved.

• This is done by:
– Emphasis on continuous feedback from the customer
– Short iterations
– Design and redesign
– Coding and testing frequently
– Eliminating defects early, thus reducing costs
– Keeping the customer involved throughout the
development
– Delivering working product to the customer

• Management-Practices
– On-Site Customer: A central customer contact must always be
accessible in order to clarify requirements and questions
directly.
– Planning Game: Projects, in accordance with XP, run iteratively
(repeatedly) and incrementally (gradually build on each other).
The contents of the next step are planned before each iteration.
All project members (incl. the customer) participate.
– Short Releases: New deliveries should be made at short
intervals. Consequently, customers receive the required
functions quicker and can therefore give feedback on the
development quicker.

• Team-Practices
– Metaphor: Only a few clear metaphors should describe the system
being developed so that the nitty-gritty of the system is clear to all of
the project members.
– Collective Ownership: The whole team is responsible for the system,
not individuals. Each developer must have access to all lines of code so
that each developer is able to take over the task of another developer.
– Continuous Integration: All changes to the system are integrated
promptly so that not too many dependencies between changes occur.
– Coding Standards: Regarding the common responsibility for the code,
there should be a given common standard for writing the code.
– Sustainable Pace: XP builds on the creativity of the individual project
members. This creativity cannot be achieved if the project team
constantly works overtime. Overtime is to be avoided.

• Programming-Practices
– Testing: All developments must be tested.
– Simple Design: The system should be designed as simply
as possible so that it is easier to understand, modify and
test.
– Refactoring: As soon as it becomes necessary to alter the
structure of the system, it should be implemented.
– Pair Programming: There are always two developers sitting
in front of a computer in order to increase the quality and
transfer the knowledge better.

• Project are broken down into 1-2 week
iterations.
• If changes occur in the middle of an iteration,
the team are capable of reacting to them, as
long as the team hasn’t started work on a
particular feature.
• Extreme Programming teams work in a strict
priority order. Features to be developed are
prioritized by the customer.

• Design
– Writing unit tests before programming and
keeping all of the tests running at all times. The
unit tests are automated and eliminates defects
early, thus reducing the costs.
– Starting with a simple design just enough to code
the features at hand and redesigning when
required.

• Design: User Stories

• Development
– Programming in pairs (called pair programming),
with two programmers at one screen, taking turns
to use the keyboard. While one of them is at the
keyboard, the other constantly reviews and
provides inputs.
– Integrating and testing the whole system several
times a day.

• Pair Programming
– two programmers work together at one
workstation.
– One, the driver, writes code while the other, the
observer or navigator, reviews each line of code
as it is typed in.
– The two programmers switch roles frequently.

– While reviewing, the observer also considers the
"strategic" direction of the work, coming up with
ideas for improvements and likely future problems
to address.
– This frees the driver to focus all of their attention
on the "tactical" aspects of completing the current
task, using the observer as a safety net and guide.

– Pair programming increases the man-hours
required to deliver code compared to
programmers working individually from up to
between 15% and 100%.
– However, the resulting code has about 15% fewer
defects.

• Production
– Putting a minimal working system into the
production quickly and upgrading it whenever
required.
– Keeping the customer involved all the time and
obtaining constant feedback.

Advantages
• Large project are divided into manageable
amounts

Advantages
• Reduced costs and time required for project
realization.

Advantages
• Extreme Programming teams save lots of
money because they don’t use too much
documentation.

Advantages
• Simplicity is another advantage of Extreme
Programming projects.

Advantages
• XP is reduces the risks related to
programming. Normally programming
depends a lot on individuals key team
members. In XP, Using module structure, and
pair programing XP spreads the risk and
mitigate the dependence on individuals

Advantages
• In software simplicity always brings quality
and contributes the robustness. By bringing
simplicity, XP manages to create faster
software with less defects.
Test driven development at the coding stage
and the customer UAT validation leads to
successful development completion.

Disadvantages
• Extreme Programming is focused on the code
rather than on design.

Disadvantages
• XP requires a detailed planning from the start
due to changing costs & scope

Disadvantages
• XP doesn't measure/plan Quality Assurance of
coding.

Disadvantages
• To convince developers to accept this tough
practice is not always easy. It requires more
discipline in the team and devotion of your
customers. Project management might
experience difficulties related with
the practice that changes during the life
cycle.

Disadvantages
• XP is practiced with pair programming which
might usually lead to too much duplication of
codes and data.

Interesting
• XP engineering practices include things like
test-driven development, automated testing,
pair programming, simple design, and
refactoring.

Interesting
• XP says that the only truly important product
of the system development process is code.

Interesting
• Coding can also help to communicate
thoughts about programming problems. A
programmer dealing with a complex
programming problem, or finding it hard to
explain the solution to fellow programmers,
might code it in a simplified manner and use
the code to demonstrate what she means.

Interesting
• System-wide integration testing is
encouraged, initially, as a weekly activity, for
early detection of incompatible interfaces, to
reconnect before the separate sections
diverged widely from coherent functionality.

Interesting
• Listening is a key element of XP, programmers
must listen to what the customers need the
system to do, what "business logic" is needed.

Interesting
• XP is still evolving, assimilating more lessons
from experiences in the field. In the second
edition of Extreme Programming Explained,
five years after the first edition, Beck added
more values and practices and differentiated
between primary and corollary practices.

Interesting
There are other versions of the Model:

Reflections
• XP is very useful when we have:
– Dynamically changing software requirements
– Risks caused by fixed time projects using new
technology
– Small, co-located extended development team
– The technology you are using allows for
automated unit and functional tests

Reflections
• XP sees communication as a vital aspect of
development, and most people agree that
face to face conversation is the best form of
communication, so XP suggests that the team
sit together in the same space without
barriers to communication, such as cubicle
walls.

Reflections
• XP tells you to build in some slack, the idea
behind slack is to add some low priority tasks
or stories in your weekly and quarterly cycles
that can be dropped if the team gets behind
on more important tasks or stories.

Reflections
• XP focuses on practice excellence. The method
prescribes a small number of absolutely
essential practices and encourages teams to
perform those practices as good as they
possibly can, almost to the extreme.

The Extreme Programming (XP) Model

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