SOFTWARE ENGINEERING
(CS3529)
TARGET CLASSES: CS14: A,B
Lecturer:
Eng. Mohamed Adam Isak
PH.D Researcher in CS
M.Sc. and B.Sc. of Information Technology Engineering,
Lecturer in University of Somalia and Mogadishu university
E-mail: [email protected].
Tell:0615648915
WWW.ENGMAISAK.BLOGSPOT.COM
February – July 2016
CHAPTER 3 – AGILE SOFTWARE DEVELOPMENT
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TOPICS COVERED
• Plan-driven and agile development
• The principles of agile methods
•
Technical, human, organizational issues
• Extreme programming
• Scrum approach
•
Agile project management
• Scrum approach and scrum processes
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RAPID SOFTWARE DEVELOPMENT
•
Rapid development and delivery is now often the most important requirement for software
systems
• Businesses operate in a fast –changing requirement and it is practically impossible to
produce a set of stable software requirements
• Software has to evolve quickly to reflect changing business needs.
•
Although there are many approaches to rapid software development, they share these three
fundamental characteristics:
1. The processes of Specification, design and implementation are inter-leaved.
2. The system is developed as a series of versions with stakeholder’s feedback.
3. User interfaces are often developed using an interactive development system that
allows the interface design to be quickly .
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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:
• Focus on the code rather than the design
• Are based on an iterative approach to software development
• Are intended to deliver working software quickly 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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THE PRINCIPLES OF AGILE METHODS
 Although agile methods are all based around incremental development and delivery,
they propose different processes to achieve this, however, they share a set of principles.
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 specifying the
requirements to 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
Expect the system requirements to change and so design the system to
accommodate these changes.
Maintain simplicity
Focus on simplicity in both the software being developed and in the
development process. Wherever possible, actively work to eliminate
complexity from the system.
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AGILE METHODS APPLICABILITY
 Agile methods have been very successful for some types of system development:
1. Product development where a software company is developing a small or mediumsized product for sale.
2. Custom system development within an organization, where there is a clear
commitment from the customer to become involved in the development process and
where 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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PROBLEMS WITH AGILE METHODS
•
It can be difficult to keep the interest of customers who are involved in the process.
•
Team members may be unsuited to the intense involvement that characterizes agile
methods.
•
Prioritizing changes can be difficult where there are multiple stakeholders.
•
Maintaining simplicity requires extra work.
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PLAN-DRIVEN VS AGILE DEVELOPMENT
•
Plan-driven development
• 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.
• Iteration occurs within activities.
•
Agile development
• Specification, design, implementation and testing are inter-leaved and the outputs from the
development process are decided through a process of negotiation during the software
development process.
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TECHNICAL, HUMAN, ORGANIZATIONAL ISSUES
 In fact, most software projects include practices from plan-driven and agile approaches. To decide on
the balance between a plan-based and an agile approach, you have to answer a range of technical,
human, and organizational questions:
1. Is it important to have a very detailed specification and design before moving to
implementation? If so, you probably need to use a plan-driven approach.
2. Is an incremental delivery strategy, where you deliver the software to customers and get rapid
feedback from them, realistic? If so, consider using agile methods.
3. How large is the system that is being developed? Agile methods are most effective when the
system can be developed with a small co-located team who can communicate informally. This
may not be possible for large systems that require larger development teams so a plan -driven
approach may have to be used.
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TECHNICAL, HUMAN, ORGANIZATIONAL ISSUES
4. What type of system is being developed?
•
Plan-driven approaches may be required for systems that require a lot of analysis
before implementation (e.g. real-time system with complex timing requirements).
5. What is the expected system lifetime?
•
Long-lifetime systems may require more design documentation to communicate the
original intentions of the system developers to the support team.
6. What technologies are available to support system development?
•
Agile methods rely on good tools to keep track of an evolving design
7. How is the development team organized?
•
If the development team is distributed or if part of the development is being
outsourced, then you may need to develop design documents to communicate across
the development teams.
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TECHNICAL, HUMAN, ORGANIZATIONAL ISSUES
8. Are there cultural or organizational issues that may affect the system development?
•
Traditional engineering organizations have a culture of plan-based
development, as this is the norm in engineering.
9. How good are the designers and programmers in the development team?
•
It is sometimes argued that agile methods require higher skill levels than planbased approaches in which programmers simply translate a detailed design
into code
10. Is the system subject to external regulation?
•
If a system has to be approved by an external regulator then you will probably
be required to produce detailed documentation as part of the system safety
case.
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EXTREME PROGRAMMING (XP MODEL)
•
Extreme programming (XP) is perhaps the best known and most widely used of the
agile methods.
•
The name was coined by Beck (2000) because the approach was developed by
pushing recognized good practice, such as iterative development, to ‘extreme’ levels.
•
Extreme Programming (XP) takes an ‘extreme’ approach to iterative development.
• New versions may be built several times per day;
• Increments are delivered to customers every 2 weeks;
• All tests must be run for every build and the build is only accepted if tests run
successfully.
• In an XP process, customers are involved in specifying and prioritizing requirements.
• in XP, the new versions may be developed by different programmers in different
locations.
• Requirements in eXtreme Programming (XP) Called: scenarios or user stories
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THE EXTREME PROGRAMMING RELEASE CYCLE
(PHASES OF XP MODEL)
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EXTREME PROGRAMMING PRACTICES (1/2)
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.
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 (2/2)
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
all the developers take responsibility for all of the code. Anyone
can change anything.
Continuous integration
As soon as the work on a task is complete, it is integrated into
the whole system. After any such integration, all the unit tests in
the system must pass.
On-site customer
The customer should be available full time with the XP team. He
is responsible for specifying system requirements.
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XP AND CHANGE
•
Conventional wisdom in software engineering is to design for change. It is worth spending
time and effort anticipating changes as this reduces costs later in the life cycle.
•
XP solves problem of changing using constant code improvement (refactoring) which is
responsible for making changes easier when they have to be implemented.
•
Refactoring is a process of software improvement. Examples of refactoring include the
reorganization of a class hierarchy to remove duplicate code, the tidying up and renaming
of attributes and methods, and the replacement of code with calls to methods defined in a
program library.
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THE CHARACTERISTICS OF TESTING IN XP
•
The three important characteristics of extreme programming are:
1. Requirements expressed as scenarios,
2. Pair programming,
3. Test-first development. Means When a system feature is identified, the tests of
the code implementing that feature are written before the code. Tests are
automated and all tests are run when a new increment is added to the system.
•
The possible problems of test-first development are:
• Programmers may take short-cuts when developing tests so that the system
tests are incomplete.
• Some tests can be difficult to write incrementally. It is difficult to estimate the
completeness of a test set.
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ADVANTAGES OF PAIR PROGRAMMING
•
The use of pair programming has a number of advantages:
1. It supports the idea of collective ownership and responsibility for the system .
2. It acts as an informal review process because each line of code is looked at by at
least two people.
3. It helps support refactoring, which is a process of software improvement.
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AGILE PROJECT MANAGEMENT
•
The principal responsibility of software project managers is to manage the project so that
the software is delivered on time and within the planned budget for the project. They
supervise the work of software engineers and monitor how well the software development
is progressing
•
The standard approach to project management is plan-driven
•
Like every other professional software development process, agile development has to be
managed so that the best use is made of the time and resources available to the team.
This requires a different approach to project management, which is adapted to
incremental development and the particular strengths of agile methods.
•
SCRUM is one of the usable approaches to manage agile development.
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SCRUM APPROACH AND SCRUM PROCESSES
•
The Scrum approach is a general agile method but its focus is on managing iterative
development rather than specific technical approaches to agile software engineering.
•
A Scrum sprint is a planning unit in which the work to be done is assessed, features are
selected for development, and the software is implemented. At the end of a sprint, the
completed functionality is delivered to stakeholders.
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SCALING AGILE METHODS
•
Agile methods were developed for use by small programming teams who could work
together in the same room and communicate informally.
•
It is difficult to introduce agile methods into large companies for a number of reasons:
1. Project managers who do not have experience of agile methods may be reluctant to
accept the risk of a new approach, as they do not know how this will affect their
particular projects
2. Large organizations often have quality procedures and standards that all projects
are expected to follow
3. Agile methods seem to work best when team members have a relatively high skill
level
4. There may be cultural resistance to agile methods, especially in those organizations
that have a long history of using conventional systems engineering processes.
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KEY POINTS
•
Agile methods are incremental development methods that focus on rapid development,
frequent releases of the software, reducing process overheads and producing high -quality
code. They involve the customer directly in the development process.
•
The decision on whether to use an agile or a plan-driven approach to development should
depend on the type of software being developed, the capabilities of the development team
and the culture of the company developing the system.
•
Extreme programming is a well-known agile method that integrates a range of good
programming practices such as frequent releases of the software, continuous software
improvement and customer participation in the development team.
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