CEN 4021
Software Engineering II
Software Process Models
Instructor: Masoud Sadjadi
http://www.cs.fiu.edu/~sadjadi/
sadjadi@cs.fiu.edu
CEN 4021
2nd Lecture
Acknowledgements

Dr. Onyeka Ezenwoye

Dr. Peter Clarke

Dr. Betty Cheng

Dr. Bernd Bruegge

Dr. Allen Dutoit
CEN 4021: Software Engineering II
2nd Lecture
2
Objectives

To understand
– Software process and process models,
including the main characteristics of each
model, critical software process issues, and the
pros and cons of each model.
– The generic process activities and what they
mean. This includes details of what exactly
each activity is for and the stages within them.
CEN 4021: Software Engineering II
2nd Lecture
The software process

A structured set of activities required to develop a
software system
– Specification;
– Design;
– Validation;
– Evolution.

A software process model is an abstract
representation of a process. It presents a
description of a process from some particular
perspective.
CEN 4021: Software Engineering II
2nd Lecture
Abstraction

Elimination of unnecessary detail

CEN 4021: Software Engineering II
Model
 Abstract view
 Abstract representation
2nd Lecture
Software Process model
A
software process model is an
abstract representation of a process. It
presents a description of a process
from some particular perspective.
 No universal software process
 Highly intellectual
 Must dynamically adjust to creative
needs of professionals and tasks
CEN 4021: Software Engineering II
2nd Lecture
Critical Software Process Issues
 Factors
to consider
– Nature of the project.
 Software
projects are different.
– Organizational needs.
– Experience level of members/team
– Current product status
 E.g.,
Brand new product?
– Available tools and facilities
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Critical Software Process Issues
 Factors
to consider
– Quality
 More
intensive quality assurance
– Product Technology
 New
technology or algorithm?
– Requirements instability
 Unknown
requirements
 Unstable requirements
– Complexity
 Large
systems
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2nd Lecture
Software Process Models
 Waterfall
V
 Spiral
 Rapid
Application Development
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2nd Lecture
Waterfall model
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2nd Lecture
Waterfall model phases
Requirements analysis and definition
 System and software design
 Implementation and unit testing
 Integration and system testing
 Operation and maintenance
 The main drawback of the waterfall model is
the difficulty of accommodating change
after the process is underway. One phase
has to be complete before moving onto the
next phase.

CEN 4021: Software Engineering II
2nd Lecture
Waterfall model problems
Inflexible partitioning of the project into
distinct stages makes it difficult to respond to
changing customer requirements.
 Therefore, this model is only appropriate
when the requirements are well-understood
and changes will be fairly limited during the
design process.
 Few business systems have stable
requirements.
 Requirements have to be understood early
on.

CEN 4021: Software Engineering II
2nd Lecture
V-Shaped Model
Project and
Requirement
s Planning
Production
Operation and
Maintenance
Product
Requirements
and
Specification
Analysis
Architecture or
High-Level
Design
System and
Acceptance
Testing
Integration
and Testing
Detailed
Design
Unit Testing
Coding
CEN 4021: Software Engineering II
2nd Lecture
V-Shaped Model





A variation of the Waterfall model.
Places strong emphasis on Verification and Validation.
Testing of the product is planned in the early phases of the
process.
Acceptance test plan is developed.
System test plan is developed.
CEN 4021: Software Engineering II
2nd Lecture
V-Shaped Model


Emphasizes the relationship between the phases
preceding and following coding.
The dotted lines indicate that these phases should be
considered in parallel.
CEN 4021: Software Engineering II
2nd Lecture
Phases in the V-Shaped Model

Project and requirements planning
– Determines system requirements and allocation of resources.

Product requirements and specification analysis
– Analysis of software problem, concludes with complete
specification of the software.
CEN 4021: Software Engineering II
2nd Lecture
Phases in the V-Shaped Model

Architecture or High-level design
– Determines how the software functions are to implement the
design.

Detailed Design
– Defines algorithms for components that were defined during the
architecture phase.
CEN 4021: Software Engineering II
2nd Lecture
Phases in the V-Shaped Model

Coding
– Transforms the algorithms defined during the design phase into
software.

Unit Testing
– Checks each code module for errors.
CEN 4021: Software Engineering II
2nd Lecture
Phases in the V-Shaped Model

Integration and Testing
– Integrate and test individual code modules.

System and acceptance testing
– Test entire software system in its hardware
environment.
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Phases in the V-Shaped Model

Productions, operation and maintenance
– Puts software into production and provides for enhancements
and corrections.
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V-Shaped Model Problems
Does not easily handle concurrent events
 No iteration of phases
 Cannot handle dynamic changes in
requirements throughout the life cycle
 Requirements are tested too late to make
changes without affecting the schedule
 No risk analysis

CEN 4021: Software Engineering II
2nd Lecture
Spiral development
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.

CEN 4021: Software Engineering II
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process
Determine objectives,
alternatives and
constraints
Evaluate alternatives,
identify, resolve risks
Operational
prototype
requirements
Plan next phase
And test plan
Develop, verify next-level
product
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2nd Lecture
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.
CEN 4021: Software Engineering II
2nd Lecture
Spiral Model problems

Highly dependent on risk analysis
– Requires very knowledgeable personnel
– Errors may occur if risk is not properly analyzed

Willingness of the Customer
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RAD Model

Rapid Application Development

User is involved in all phases
Use tools that allow product evaluation at all
stages of development
Characterized by quick turnaround time from
requirements definition to delivery
High component reuse factor



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RAD Model
Development Effort
User
Involvement
Construction
User
Description
Requirements
Planning
Cut
Over
Time
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Phases in RAD Model

Requirements planning phase
– Requirements are gathered using technique called joint
requirements planning (JRP)

User description
– Joint application design (JAP) is used to harness user
involvement.
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Phases in RAD Model

Construction phase
– Combines design, coding, testing. Heavy use of code
generators and other production tools

Cut over
– Acceptance testing, installation and user training.
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Strengths of RAD
Use of powerful tools reduces cycle time
 Lower cost due to reduced cycle time
 Ongoing customer involvement
 Reuse of existing program component

CEN 4021: Software Engineering II
2nd Lecture
RAD problems
Heavily dependent on user involvement
throughout the process.
 Requires highly skilled developers in the
use of development tools.
 Heavily dependent on reusable
components.

CEN 4021: Software Engineering II
2nd Lecture
Generic activities
Specification
 Design (and implementation)
 Validation
 Evolution

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2nd Lecture
Specification
The process of establishing what services
are required and the constraints on the
system’s operation and development.
 Requirements engineering process

– Feasibility study;
– Requirements elicitation and analysis;
– Requirements specification;
– Requirements validation.
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example requirements
engineering process
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design and implementation
The process of converting the system
specification into an executable system.
 design

– Design a software structure that realises the
specification;

Implementation
– Translate this structure into an executable
program;

The activities of design and implementation
are closely related and may be inter-leaved.
CEN 4021: Software Engineering II
2nd Lecture
example design process activities
Architectural design
 Abstract specification
 Interface design
 Component design
 Data structure design
 Algorithm design

CEN 4021: Software Engineering II
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example software design process
CEN 4021: Software Engineering II
2nd Lecture
Validation
Verification and validation (V & V) is
intended to show that a system conforms to
its specification and meets the requirements
of the system customer.
 Involves checking and review of processes,
various testing stages.
 Testing involves executing the system with
test cases that are derived from the
specification.
 Testing tries to establish if observed
behaviour matches expected behaviour.

CEN 4021: Software Engineering II
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Testing stages

Unit testing
– Individual components are tested independently;
– Components may be functions or objects or coherent
groupings of these entities.

Integration testing (subsystem testing)
– Individual components are merged and tested.

System testing
– Testing of the system as a whole. Testing of emergent
properties is particularly important.

Acceptance testing
– Testing with customer data to check that the system
meets the customer’s needs.
CEN 4021: Software Engineering II
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Testing phases
note that model is V
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Evolution
Software is inherently flexible and can
change.
 As requirements change through changing
business circumstances, the software that
supports the business must also evolve and
change.
 Although there has been a demarcation
between development and evolution
(maintenance) this is increasingly irrelevant
as fewer and fewer systems are completely
new.

CEN 4021: Software Engineering II
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Example evolution process
CEN 4021: Software Engineering II
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