Chapter 2 – Software Processes

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Topics covered
² Process activities
² Software process models
² Coping with change
² The Rational Unified Process
§  An example of a modern software process.

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The software process
² A structured set of activities required to develop a

software system.
² Many different software processes but all involve:
§ 
§ 
§ 
§ 

Specification
Design and implementation
Validation
Evolution

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Software specification
² The process of establishing
§  what services are required
§  and the constraints on the system’s operation and development.

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The requirements engineering process

Feasibility
study

Requirements
elicitation and
analysis

Requirements
specification
Requirements
validation

Feasibility
report
System
models
User and system
requirements

Requirements
document


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System models

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Software design and implementation
² The process of converting the system specification into
an executable system.
Đ Software design
ã Design a software structure that realises the specification;

Đ Implementation
ã Translate this structure into an executable program;

² The activities of design and implementation are closely
related and may be interleaved.

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A general model of the design process

Design inputs
Platform
information


Data
description

Requirements
specification

Design activities
Architectural
design

Interface
design

Component
design

Database design

Design outputs
System
architecture

Database
specification

Interface
specification

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Component
specification

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Design activities
² Architectural design: identify the overall structure, the
principal components, their relationships and how they
are distributed.
² Interface design: define the interfaces between system
components.
² Component design: take each system component and
design how it will operate.
² Database design: design the system data structures
and how these are to be represented in a database.

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Implementation
² Programming is a personal activity and there is no
general process that is usually followed.
² The development of a program to implement the system
follows naturally from the system design processes.
² Programmers carry out some testing of the code to
reveal program defects that must be removed from the
program. This is called debugging.

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Software validation
² Verification and validation (V & V) is intended to show
that a system conforms to its specification and meets
the requirements of the system customer.
² Involves checking and review processes and system
testing.
² System testing involves executing the system with test
cases that are derived from the specification of the real

data to be processed by the system.
² Testing is the most commonly used V & V activity.

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Stages of testing

Component
testing

System testing

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Acceptance
testing

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Write unit tests with JUnit
Class
 and
 method
 
• 

Test
 case
 

public
 class
 Person
 {
 
private
 String
 firstName;
 
private
 String
 lastName;
 

 
public

 Person(String
 firstName,
 String
 lastName)
 {
 
if
 (firstName
 ==
 null
 &&
 lastName
 ==
 null)
 {
 
throw
 new
 IllegalArgumentExcepPon("Both
 names
 
cannot
 be
 null");
 
}
 
this.firstName
 =
 firstName;

 
this.lastName
 =
 lastName;
 
}
 
public
 String
 getFullName()
 {
 
String
 first
 =
 (this.firstName
 !=
 null)
 ?
 this.firstName
 :
 
"?";
 
String
 last
 =
 (this.lastName
 !=
 null)

 ?
 this.lastName
 :
 "?";
 

 
return
 first
 +
 last;
 


 

 

 
}

• 

• 

import
 junit.framework.TestCase;
 

 


 
public
 class
 TestPerson
 extends
 TestCase
 {
 
public
 TestPerson(String
 name)
 {
 
super(name);
 
}
 

 
/**
 
Confirm
 that
 the
 name
 is
 shown
 in
 correct

 
forma`ed?
 
 *
 */
 
public
 void
 testGetFullName()
 {
 
Person
 p
 =
 new
 Person("Aidan",
 "Burke");
 
assertEquals("Aidan
 Burke",
 
p.getFullName());
 
}
 


 

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Testing stages
² Development or component testing
§  Individual components are tested independently;
§  Components may be functions or objects or coherent groupings
of these entities.

² System testing
§  Testing of the system as a whole. Testing of emergent properties
is particularly important.

² Acceptance testing
§  Testing with customer data to check that the system meets the
customer’s needs.

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Software evolution
² Software is inherently flexible and can change.
² As requirements change through changing business
circumstances, the software that supports the business
must also evolve and change.
² Although there has been a demarcation between
development and evolution (maintenance) this is
increasingly irrelevant as fewer and fewer systems are
completely new.

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System evolution

Define system
requirements

Assess existing
systems


Propose system
changes

Existing
systems

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Modify
systems

New
system

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Process activities
² Real software processes are inter-leaved sequences of
§  Technical activites
§  Collaborative activities
§  Managerial activities

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Testing phases in a plan-driven software
process

Requirements
specification

System
specification

System
integration
test plan

Acceptance
test plan

Service

System
design


Acceptance
test

Detailed
design

Sub-system
integration
test plan

System
integration test

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Module and
unit code
and test

Sub-system
integration test

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Software process descriptions
² Usually includes
§  Activities ( specifying a data model, designing a user interface,
etc.)
§  Ordering of these activities.

² Also include:
§  Products
§  Roles
§  Pre- and post-conditions,

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Software process model
² A software process model is an abstract representation
of a process. It presents a description of a process from
some particular perspective.
² For example: from an architectural perspective. That
is, we see the framework of the process but not the
details of specific activities (waterfall model, incremental
development)


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Plan-driven and agile processes
² Plan-driven processes are processes where all of the
process activities are planned in advance and progress
is measured against this plan.
² In agile processes, planning is incremental and it is
easier to change the process to reflect changing
customer requirements.
² In practice, most practical processes include elements of
both plan-driven and agile approaches.
² There are no right or wrong software processes.

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Software process models
² The waterfall model
§  Plan-driven model. Separate and distinct phases of specification
and development.

² Incremental development
§  Specification, development and validation are interleaved. May
be plan-driven or agile.

² Reuse-oriented software engineering
§  The system is assembled from existing components. May be
plan-driven or agile.

² In practice, most large systems are developed using a
process that incorporates elements from all of these
models.
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The waterfall model

Requirements

definition
System and
software design

Implementation
and unit testing
Integration and
system testing
Operation and
maintenance

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Waterfall model phases
² There are (5) separate identified phases in the waterfall
model:
§ 
§ 
§ 
§ 
§ 


Requirements analysis and definition
System and software design
Implementation and unit testing
Integration and system testing
Operation and maintenance

² In principle, a phase has to be complete before moving
onto the next phase.

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