Software Engineering


Software Engineering

- Abdul Majeed

Contents of the Seminar

What is software?

Definition of Software Engineering

Software Process

Generic view of Software Engineering

Software Process Paradigms

Software Testing Strategies

What is software?

• Computer documentation programs and associated

• Software products may be developed for a particular customer or may be developed for a general market

• Software products may be

– Generic developed to be sold to a range of different customers

– Bespoke (custom) - developed for a single customer according to their specification

What is software engineering?

Software engineering is an engineering discipline which is concerned with all aspects of software production (development and maintenance).

In general sense the product will exist three times of the development duration so the total efforts will be distributed as 30/70 or 40/60 for development and maintenance respectively.

Economic and Management aspects of SE

• Software production = development + maintenance (evolution)

• Development costs will be 40%

– 40% analysis and design

– 20% coding

– 40% testing

• Maintenance costs > 60% of all development costs

– 20% corrective

– 30% adaptive

– 50% perfective

• Quicker development is not always preferable

– higher up-front costs may defray downstream costs

– poorly designed/implemented software is a critical cost factor

Economic and Management aspects of SE















What is the difference between software engineering and computer science?

Computer Science Software Engineering

is concerned with

 theory

 fundamentals

 the practicalities of developing

 delivering useful software

Computer science theories

are currently insufficient to act as a complete underpinning for software engineering, BUT it is a foundation for practical aspects of software engineering

What is the difference between software engineering and system engineering?

• Software engineering is part of System engineering

• System engineering is concerned with all aspects of computer-based systems development including

– hardware,

– software and

– process engineering

• System engineers are involved in system specification, architectural design , integration and deployment

What is a software process?

A set of activities whose goal is the development or evolution of software

Generic activities in all software processes are:

Specification what the system should do and its development constraints

Development production of the software system

Validation checking that the software is what the customer wants

Evolution changing the software in response to changing demands

Generic view of SE

There are Three Phases of any software process

1. Definition phase which include activities such as

- System/Information engineering

- Software project planning

- Requirement analysis

2 . Development phase which include activities such as

- Design

- Coding

- Testing

3. Maintenance which include activities such as

- Fixing the bugs

- Adaptation

- Enhancement

Software Process Paradigms

Different categories of software process paradigms are

- Classical Life Cycle Model/ Linear

Sequential Model/Waterfall Model

- Prototype Model

- Rapid Application Development

Model (RAD)

- Evolutionary Model (Incremental and

Spiral Model)

- Component based model

- Formal Transformation

Software Development Lifecycle

Waterfall Model







Software Development Lifecycle

Spiral Model

Determine objectives alternatives, constraints

Evaluate alternatives, identify, resolve risks, develop prototypes

Develop, verify next-level product

Plan next phases


Problem Definition → Requirements


determine exactly what the customer and user want

develop a contract with the customer

specifies what the software product is to do


client asks for wrong product

client is computer/software illiterate

specifications are ambiguous, inconsistent, incomplete


Requirements Specification


architecture: decompose software into modules with interfaces

design: develop module specifications

(algorithms, data types)

maintain a record of design decisions and traceability

specifies how the software product is to do its tasks


miscommunication between module designers

design may be inconsistent, incomplete, ambiguous

Architecture vs. Design

Architecture is concerned with the selection of architectural elements , their interactions, and the constraints on those elements and their interactions necessary to provide a framework in which to satisfy the requirements and serve as a basis for the design.

Design is concerned with the modularization and detailed interfaces of the design elements, their algorithms and procedures, and the data types needed to support the architecture and to satisfy the requirements.

Implementation & Integration

Design → Implementation

implement modules; verify that they meet their specifications

combine modules according to the design

specifies how the software product does its tasks


module interaction errors

order of integration may influence quality and productivity

Software Testing Strategy

Testing is categorized into

Unit Testing verifies the coding of the product

Integration Testing verifies the design of the product

Validation Testing verifies the requirement

System Testing verifies system engineering

Software Testing Strategy

System testing

Validation testing

Integration testing

Unit testing




System engineering

Software Testing Strategy

Integration testing includes

Top down using stubs

- Bottom up using drivers

Validation testing includes

Alpha testing

- Beta testing

System testing includes

Recovery testing

- Security testing

- Stress testing

- Performance testing