Software Engineering
The Software Process (2)
The Waterfall Model
Requirements
Definition
System and
Software design
Programming
and Unit Testing
Integration and
System Testing
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Operation and
Maintenance
Incremental development
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Evolutionary Process Model
Concurr ent
activities
Outline
description
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Specification
Initial
version
Development
Intermediate
versions
Validation
Final
version
Spiral development
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Process is represented as a spiral rather than as a
sequence of activities with backtracking.
Each loop in the spiral represents a phase in the
process.
No fixed phases such as specification or design loops in the spiral are chosen depending on what
is required.
Risks are explicitly assessed and resolved
throughout the process.
Spiral Model
material adapted from Steve Easterbrook
Determine goals,
alternatives,
constraints
budget4
Evaluate
alternatives
and risks
budget3
budget2
budget1
prototype1
prototype2
prototype3 prototype4
Develop
and
test
Plan
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Details of the Spiral
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Boehm’s Spiral Lifecycle
Planning = determination
of objectives, alternatives
and constraints
initial requirements
Risk Analysis = Analysis of
alternatives and identification/
resolution of risks
Risk = something that
will delay project or
increase its cost
go, no-go decision
completion
first prototype
alpha demo
Customer Evaluation =
Assessment of the
results of engineering
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evolving system
Engineering =
Development of the
next level product
Spiral model sectors
 Objective setting
Specific objectives for the phase are identified.
 Risk assessment and reduction
Risks are assessed and activities put in place to reduce the
key risks.
 Development and validation
A development model for the system is chosen which can be
any of the generic models.
 Planning
The project is reviewed and the next phase of the spiral is
planned.
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The spiral model
The Risk Management Plan
 Identify the project’s top 10 risk items.
 Present a plan for resolving each risk item.
 Update list of top risk items, plan, and results monthly.
 Highlight risk-item status in monthly project reviews.
Compare with previous month’s rankings, status.
 Initiate appropriate corrective actions.
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Spiral Model Advantages
Focuses attention on reuse options.
Focuses attention on early error elimination.
Puts quality objectives up front.
Integrates development and maintenance.
Provides a framework for hardware/software
development.
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Prototyping Model
material adapted from Steve Easterbrook
Preliminary
design
requirements prototype
build
prototype
Specify full
requirements
evaluate
prototype
design
code
 Prototyping is used for:
 Understanding the requirements for the user interface
 Examining feasibility of a proposed design approach
 Exploring system performance issues
 Problems
 Users treat the prototype as the solution
 A prototype is only a partial specification
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test
integrate
V Model
Level of abstraction
material adapted from Steve Easterbrook
system
requirements
system
integration
software
requirements
acceptance
test
preliminary
design
“analyze
and
design”
detailed
design
code and
debug
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software
integration
“test
and
integrate”
component
test
unit
test
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time
V Model
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V- model means Verification and Validation
model.
Just like the waterfall model, the V-Shaped life
cycle is a sequential path of execution of
processes.
Each phase must be completed before the next
phase begins.
Testing of the product is planned in parallel with a
corresponding phase of development.
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V Model
Requirements begin the life cycle model
just like the waterfall model.
But, in this model before development is
started, a system test plan is created.
The test plan focuses on meeting the
functionality specified in the requirements
gathering.
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Agile Model (XP)
material adapted from Steve Easterbrook
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Agile Software Development
Agile software development is a group
of software development methods type
of iterative and incremental development,
where requirements and solutions evolve
through collaboration between selforganizing, cross-functional teams.
It is used for time critical applications
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Agile Software Development
Agile Methods break the product into small
incremental builds. Each iteration typically lasts
from about one to three weeks
Every iteration involves cross functional teams
working simultaneously on various areas like
planning, requirements analysis, design, coding,
unit testing, and acceptance testing.
At the end of the iteration a working product is
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displayed to the customer and important
Agile Software Development
 It promotes adaptive planning,
evolutionary development and
delivery, a time-boxed iterative
approach, and encourages
rapid and flexible response to
change.
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What is Agility?
Effective response to change
Effective communication among all
stakeholders
Drawing the customer onto the team;
eliminate the “us and them” attitude
Organizing a team so that it is in control of
the work performed
Rapid, incremental delivery of software
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The Agile Principles
Our highest priority is to satisfy the customer through
early and continuous delivery of valuable software.
Welcome changing requirements, even late in
development. Agile processes harness change for the
customer’s competitive advantage.
Deliver working software frequently, from a couple of
weeks to a couple of months, with a preference to the
shorter timescale.
Business people and developers must work together
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daily throughout the project.
The Agile Principles
Build projects around motivated individuals. Give them
the environment and support they need, and trust them to
get the job done.
The most efficient and effective method of conveying
information to and within a development team is face-toface conversation.
Working software is the primary measure of progress.
Agile processes promote sustainable development. The
sponsors, developers, and users should be able to maintain
25a constant pace indefinitely.
The Agile Principles
Continuous attention to technical excellence and good
design enhances agility.
Simplicity–the art of maximizing the amount of work not
done–is essential.
The best architectures, requirements, and designs emerge
from self-organizing teams.
At regular intervals, the team reflects on how to become
more effective, then tunes and adjusts its behavior
accordingly.
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Agile Process Models
Extreme Programming (XP)
Adaptive Software Development (ASD)
Dynamic Systems Development Method (DSDM)
Scrum
Crystal
Feature Driven Development (FDD)
Agile Modeling (AM)
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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
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build is only accepted if tests run successfully.
Extreme Programming (XP)
XP uses an object-oriented approach as its
preferred development paradigm
Defines four (4) framework activities
Planning
Design
Coding
Testing
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Extreme Programming (XP) - 2
user stories
values
acceptance test criteria
iteration plan
simple design
CRC cards
spike solutions
prototypes
refactoring
pair programming
Release
software increment
project velocity computed
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unit test
continuous integration
acceptance testing
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XP - Planning
Begins with the creation of a set of stories (also called
user stories)
Each story is placed on an index card
The customer assigns a value (i.e. a priority) to the story
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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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.
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XP - Testing
Unit tests should be implemented using a framework to
make testing automated. This encourages a regression
testing strategy.
Integration and validation testing can occur on a daily
basis
Acceptance tests, also called customer tests, are specified
by the customer and executed to assess customer visible
functionality
Acceptance tests are derived from user stories
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Reuse-oriented software engineering
 Based on systematic reuse where systems are integrated from
existing components or COTS (Commercial-off-the-shelf) systems.
 Process stages
Component analysis;
Requirements modification;
System design with reuse;
Development and integration.
 Reuse is now the standard approach for building many types of
business system
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Types of software component
Web services that are developed according to
service standards and which are available for
remote invocation.
Collections of objects that are developed as a
package to be integrated with a component
framework such as .NET or J2EE.
Stand-alone software systems (COTS) that are
configured for use in a particular environment.
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Bank example
 Requirements
 Open an account for a customer (savings or chequing)
 Deposit ƒ
Withdraw ƒ
Display details of an account ƒ
Change LOC ƒ
 Produce monthly statements ƒ
Print a list of customers
 Ambiguities
 What is the difference between savings and chequing?
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Case study
Children hospital
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Care for children in the Alexandria city and
some Arab countries
The average length of stay of inpatients is
3.6 days
All patients are accompanied by a parent
for the entire duration of their stay at
hospital
Case Study: Sensor Display
Consider a small system that displays the status of
several sensors (e.g., pressure, temperature, rate
of change, etc.) on a limited-size screen
What are some of its functional requirements?
What are some of its non-functional requirements?
display
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System
ATM system
Security
system
Branch
accounting
system
Account
database
Auto-teller
system
Branch
counter
system
Usage
database
Maintenance
system
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