Chapter 3 - Agile Software Development.ppt

Agile Software Development
 Agile methods
 Plan-driven and agile development
 Extreme programming (XP)
 Agile project management
 Pair Programming
 Scrum
 Scaling agile methods
1

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.
 Rapid software development
– Specification, design and implementation are inter-leaved
– System is developed as a series of versions with stakeholders
involved in version evaluation
– User interfaces are often developed using an IDE and graphical
toolset.
2

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.
3

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:
– 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.
4

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
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.
5

Agile method applicability
 Product development where a software company is
developing a small or medium-sized product for sale.
 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.
6

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.
 Contracts may be a problem as with other approaches
to iterative development.
7

Agile methods and software
maintenance
 Most organizations spend more on maintaining existing software
than they do on new software development. So, if agile methods
are to be successful, they have to support maintenance as well as
original development.
 Two key issues:
– Are systems that are developed using an agile approach
maintainable, given the emphasis in the development process
of minimizing formal documentation?
– Can agile methods be used effectively for evolving a system in
response to customer change requests?
 Problems may arise if original development team cannot be
maintained.
8

Plan-driven and 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.
– Not necessarily waterfall model – plan-driven, incremental
development is possible
– 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.
9

Plan-driven and agile specification
10

Technical, human, organizational
issues
 Most projects include elements of plan-driven and agile processes.
Deciding on the balance depends on:
– 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.
– 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.
– 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.
11

Technical, human, organizational
issues
– 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).
– 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.
– What technologies are available to support system development?
 Agile methods rely on good tools to keep track of an evolving design
– 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.
12

Extreme programming
 Perhaps the best-known and most widely used
agile method.
 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.
13

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.
14

The extreme programming release
cycle
15

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’. See Figures 3.5 and 3.6.
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 a new
piece of functionality before that functionality itself is implemented.
Refactoring All developers are expected to re-factor the code continuously as
16

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 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.
Sustainable pace Large amounts of overtime are not considered acceptable as the
net effect is often to reduce code quality and medium term
productivity
On-site customer A representative of the end-user of 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.
17

Requirements scenarios
 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 estimates.
18

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, however, maintains that this is not worthwhile
as changes cannot be reliably anticipated.
 Rather, it proposes constant code improvement
(refactoring) to make changes easier when they
have to be implemented.
19

Refactoring
 Programming team look for possible software improvements
and make these improvements even where there is no
immediate need for them.
 This improves the understandability of the software and so
reduces the need for documentation.
 Changes are easier to make because the code is well-
structured and clear.
 However, some changes requires architecture refactoring
and this is much more expensive.
20

Examples of refactoring
 Re-organization of a class hierarchy to remove
duplicate code.
 Tidying up and renaming attributes and
methods to make them easier to understand.
 The replacement of inline code with calls to
methods that have been included in a program
library.
21

Testing in XP
 Testing is central to XP and XP has developed an
approach where the program is tested after every
change has been made.
 XP testing features:
– Test-first development.
– Incremental test development from scenarios.
– User involvement in test development and validation.
– Automated test harnesses are used to run all
component tests each time that a new release is built.
22

Test-first development
 Writing tests before code clarifies the requirements to
be implemented.
 Tests are written as programs rather than data so that
they can be executed automatically. The test includes
a check that it has executed correctly.
– Usually relies on a testing framework such as Junit.
 All previous and new tests are run automatically when
new functionality is added, thus checking that the new
functionality has not introduced errors.
23

Customer involvement
 The role of the customer in the testing process is to help
develop acceptance tests for the stories that are to be
implemented in the next release of the system.
 The customer who is part of the team writes tests as
development proceeds. All new code is therefore validated to
ensure that it is what the customer needs.
 However, people adopting the customer role have limited time
available and so cannot work full-time with the development
team. They may feel that providing the requirements was
enough of a contribution and so may be reluctant to get
involved in the testing process.
24

Test automation
 Test automation means that tests are written as executable
components before the task is implemented
– These testing components should be stand-alone, should
simulate the submission of input to be tested and should
check that the result meets the output specification. An
automated test framework (e.g. Junit) is a system that
makes it easy to write executable tests and submit a set of
tests for execution.
 As testing is automated, there is always a set of tests that can
be quickly and easily executed
– Whenever any functionality is added to the system, the
tests can be run and problems that the new code has
introduced can be caught immediately.
25

XP testing difficulties
 Programmers prefer programming to testing and sometimes
they take short cuts when writing tests. For example, they may
write incomplete tests that do not check for all possible
exceptions that may occur.
 Some tests can be very difficult to write incrementally. For
example, in a complex user interface, it is often difficult to write
unit tests for the code that implements the ‘display logic’ and
workflow between screens.
 It difficult to judge the completeness of a set of tests. Although
you may have a lot of system tests, your test set may not
provide complete coverage.
26

Pair programming
 In XP, programmers work in pairs, sitting together to
develop code.
 This helps develop common ownership of code and spreads
knowledge across the team.
 It serves as an informal review process as each line of code
is looked at by more than 1 person.
 It encourages refactoring as the whole team can benefit
from this.
 Measurements suggest that development productivity with
pair programming is similar to that of two people working
independently.
27

Pair programming
 In pair programming, programmers sit together at the same
workstation to develop the software.
 Pairs are created dynamically so that all team members
work with each other during the development process.
 The sharing of knowledge that happens during pair
programming is very important as it reduces the overall risks
to a project when team members leave.
 Pair programming is not necessarily inefficient and there is
evidence that a pair working together is more efficient than
2 programmers working separately.
28

Advantages of pair programming
 It supports the idea of collective ownership and responsibility for the
system.
– Individuals are not held responsible for problems with the code.
Instead, the team has collective responsibility for resolving these
problems.
 It acts as an informal review process because each line of code is
looked at by at least two people.
 It helps support refactoring, which is a process of software
improvement.
– Where pair programming and collective ownership are used, others
benefit immediately from the refactoring so they are likely to support
the process.
29

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.
 The standard approach to project management is plan-driven.
Managers draw up a plan for the project showing what should
be delivered, when it should be delivered and who will work on
the development of the project deliverables.
 Agile project management requires a different approach, which
is adapted to incremental development and the particular
strengths of agile methods.
30

Scrum
 The Scrum approach is a general agile method but its focus is on
managing iterative development rather than specific agile practices.
 There are three phases in Scrum.
– The initial phase is an outline planning phase where you
establish the general objectives for the project and design the
software architecture.
– This is followed by a series of sprint cycles, where each cycle
develops an increment of the system.
– The project closure phase wraps up the project, completes
required documentation such as system help frames and user
manuals and assesses the lessons learned from the project.
31

The Sprint cycle
 Sprints are fixed length, normally 2–4 weeks. They
correspond to the development of a release of the
system in XP.
 The starting point for planning is the product backlog,
which is the list of work to be done on the project.
 The selection phase involves all of the project team
who work with the customer to select the features and
functionality to be developed during the sprint.
33

The Sprint cycle
 Once these are agreed, the team organize themselves to
develop the software. During this stage the team is isolated
from the customer and the organization, with all
communications channelled through the so-called ‘Scrum
master’.
 The role of the Scrum master is to protect the development
team from external distractions.
 At the end of the sprint, the work done is reviewed and
presented to stakeholders. The next sprint cycle then
begins.
34

Teamwork in Scrum
 The ‘Scrum master’ is a facilitator who arranges daily meetings,
tracks the backlog of work to be done, records decisions,
measures progress against the backlog and communicates with
customers and management outside of the team.
 The whole team attends short daily meetings where all team
members share information, describe their progress since the
last meeting, problems that have arisen and what is planned for
the following day.
– This means that everyone on the team knows what is going
on and, if problems arise, can re-plan short-term work to
cope with them.
35

Scrum benefits
 The product is broken down into a set of manageable and
understandable chunks.
 Unstable requirements do not hold up progress.
 The whole team have visibility of everything and
consequently team communication is improved.
 Customers see on-time delivery of increments and gain
feedback on how the product works.
 Trust between customers and developers is established and
a positive culture is created in which everyone expects the
project to succeed.
36

Scaling agile methods
 Agile methods have proved to be successful for small and
medium sized projects that can be developed by a small co-
located team.
 It is sometimes argued that the success of these methods
comes because of improved communications which is
possible when everyone is working together.
 Scaling up agile methods involves changing these to cope
with larger, longer projects where there are multiple
development teams, perhaps working in different locations.
37

Large systems development
 Large systems are usually collections of separate,
communicating systems, where separate teams develop each
system. Frequently, these teams are working in different places,
sometimes in different time zones.
 Large systems are ‘brownfield systems’, that is they include and
interact with a number of existing systems. Many of the system
requirements are concerned with this interaction and so don’t
really lend themselves to flexibility and incremental development.
 Where several systems are integrated to create a system, a
significant fraction of the development is concerned with system
configuration rather than original code development.
38

Large system development
 Large systems and their development processes are often
constrained by external rules and regulations limiting the
way that they can be developed.
 Large systems have a long procurement and development
time. It is difficult to maintain coherent teams who know
about the system over that period as, inevitably, people
move on to other jobs and projects.
 Large systems usually have a diverse set of stakeholders. It
is practically impossible to involve all of these different
stakeholders in the development process.
39

Scaling out and scaling up
 ‘Scaling up’ is concerned with using agile methods for developing
large software systems that cannot be developed by a small
team.
 ‘Scaling out’ is concerned with how agile methods can be
introduced across a large organization with many years of
software development experience.
 When scaling agile methods it is essential to maintain agile
fundamentals
– Flexible planning, frequent system releases, continuous
integration, test-driven development and good team
communications.
40

Scaling up to large systems
 For large systems development, it is not possible to focus only
on the code of the system. You need to do more up-front design
and system documentation
 Cross-team communication mechanisms have to be designed
and used. This should involve regular phone and video
conferences between team members and frequent, short
electronic meetings where teams update each other on progress.
 Continuous integration, where the whole system is built every
time any developer checks in a change, is practically impossible.
However, it is essential to maintain frequent system builds and
regular releases of the system.
41

Scaling out to large companies
 Project managers who do not have experience of agile
methods may be reluctant to accept the risk of a new approach.
 Large organizations often have quality procedures and
standards that all projects are expected to follow and, because
of their bureaucratic nature, these are likely to be incompatible
with agile methods.
 Agile methods seem to work best when team members have a
relatively high skill level. However, within large organizations,
there are likely to be a wide range of skills and abilities.
 There may be cultural resistance to agile methods, especially in
those organizations that have a long history of using
conventional systems engineering processes.
42

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