Introduction to Software Engineering: Concepts, Challenges, and Applications, Slides of Software Engineering

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CHAPTER 1- INTRODUCTION

TOPICS COVERED

◼ Professional software development

◼ What is meant by software engineering?

◼ Software engineering ethics

◼ A brief introduction to ethical issues that affect software engineering.

◼ Case studies

◼ An introduction to three examples that are used in later chapters in

the book.

SOFTWARE COSTS

◼ Software costs often dominate computer system costs. The costs

of software on a PC are often greater than the hardware cost.

◼ Software costs more to maintain than it does to develop. For

systems with a long life, maintenance costs may be several

times development costs.

◼ Software engineering is concerned with cost-effective software

development.

SOFTWARE PROJECT FAILURE

◼ Increasing system complexity

◼ As new software engineering techniques help us to build larger, more

complex systems, the demands change. Systems have to be built and

delivered more quickly; larger, even more complex systems are

required; systems have to have new capabilities that were previously

thought to be impossible.

◼ Failure to use software engineering methods

◼ It is fairly easy to write computer programs without using software

engineering methods and techniques. Many companies have drifted

into software development as their products and services have

evolved. They do not use software engineering methods in their

everyday work. Consequently, their software is often more expensive

and less reliable than it should be.

FREQUENTLY ASKED QUESTIONS ABOUT

SOFTWARE ENGINEERING

Question Answer What is software? Computer programs and associated documentation. Software products may be developed for a particular customer or may be developed for a general market. What are the attributes of good software? Good software should deliver the required functionality and performance to the user and should be maintainable, dependable and usable. What is software engineering? Software engineering is an engineering discipline that is concerned with all aspects of software production. What are the fundamental software engineering activities? Software specification, software development, software validation and software evolution. What is the difference between software engineering and computer science? Computer science focuses on theory and fundamentals; software engineering is concerned with the practicalities of developing and delivering useful software. What is the difference between software engineering and system engineering? System engineering is concerned with all aspects of computer- based systems development including hardware, software and process engineering. Software engineering is part of this more general process.

FREQUENTLY ASKED QUESTIONS ABOUT

SOFTWARE ENGINEERING

Question Answer What are the key challenges facing software engineering? Coping with increasing diversity, demands for reduced delivery times and developing trustworthy software. What are the costs of software engineering? Roughly 60% of software costs are development costs, 40% are testing costs. For custom software, evolution costs often exceed development costs. What are the best software engineering techniques and methods? While all software projects have to be professionally managed and developed, different techniques are appropriate for different types of system. For example, games should always be developed using a series of prototypes whereas safety critical control systems require a complete and analyzable specification to be developed. You can’t, therefore, say that one method is better than another. What differences has the web made to software engineering? The web has led to the availability of software services and the possibility of developing highly distributed service-based systems. Web-based systems development has led to important advances in programming languages and software reuse.

PRODUCT SPECIFICATION

◼ Generic products

◼ The specification of what the software should do is owned by the

software developer and decisions on software change are made by

the developer.

◼ Customized products

◼ The specification of what the software should do is owned by the

customer for the software and they make decisions on software

changes that are required.

ESSENTIAL ATTRIBUTES OF GOOD

SOFTWARE

Product characteristic Description Maintainability Software should be written in such a way so that it can evolve to meet the changing needs of customers. This is a critical attribute because software change is an inevitable requirement of a changing business environment. Dependability and security Software dependability includes a range of characteristics including reliability, security and safety. Dependable software should not cause physical or economic damage in the event of system failure. Malicious users should not be able to access or damage the system. Efficiency Software should not make wasteful use of system resources such as memory and processor cycles. Efficiency therefore includes responsiveness, processing time, memory utilisation, etc. Acceptability Software must be acceptable to the type of users for which it is designed. This means that it must be understandable, usable and compatible with other systems that they use.

IMPORTANCE OF SOFTWARE ENGINEERING

◼ More and more, individuals and society rely on advanced

software systems. We need to be able to produce reliable and

trustworthy systems economically and quickly.

◼ It is usually cheaper, in the long run, to use software engineering

methods and techniques for software systems rather than just

write the programs as if it was a personal programming project.

For most types of system, the majority of costs are the costs of

changing the software after it has gone into use.

SOFTWARE PROCESS ACTIVITIES

◼ Software^ specification , where customers and engineers define

the software that is to be produced and the constraints on its

operation.

◼ Software^ development , where the software is designed and

programmed.

◼ Software^ validation , where the software is checked to ensure

that it is what the customer requires.

◼ Software^ evolution , where the software is modified to reflect

changing customer and market requirements.

GENERAL ISSUES THAT AFFECT SOFTWARE

◼ Security and trust

◼ As software is intertwined with all aspects of our lives, it is essential

that we can trust that software.

◼ Scale

◼ Software has to be developed across a very wide range of scales,

from very small embedded systems in portable or wearable devices

through to Internet-scale, cloud-based systems that serve a global

community.

SOFTWARE ENGINEERING DIVERSITY

◼ There are many different types of software system and there is

no universal set of software techniques that is applicable to all of

these.

◼ The software engineering methods and tools used depend on the

type of application being developed, the requirements of the

customer and the background of the development team.

APPLICATION TYPES

◼ Batch processing systems

◼ These are business systems that are designed to process data in large

batches. They process large numbers of individual inputs to create

corresponding outputs. Examples of batch systems are periodic billing

systems, such as phone billing systems, and salary payment systems.

◼ Entertainment systems

◼ These are systems that are primarily for personal use and which are

intended to entertain the user. Most of these systems are games

◼ Systems for modeling and simulation

◼ These are systems that are developed by scientists and engineers to

model physical processes or situations, which include many, separate,

interacting objects. Example is simulators

APPLICATION TYPES

◼ Data collection systems

◼ These are systems that collect data from their environment using a

set of sensors and send that data to other systems for processing. The

software may have to interact with sensors and often is installed in a

hostile environment such as inside an engine or in a remote location.

“Big data” analysis may involve cloud-based systems carrying out

statistical analysis and looking for relationships in the collected data.

◼ Systems of systems

◼ These are systems that are composed of a number of other software

systems, such as an ERP system