Chapter 1 Introduction

Objectives

The objectives of this chapter are to introduce software engineering and to provide a framework for understanding the rest of the book. When you have read this chapter you will:

understand what software engineering is and why it is important;
understand that the development of different types of software systems may require different software engineering techniques;
understand some ethical and professional issues that are important for software engineers;
have been introduced to three systems, of different types, that will be used as examples throughout the book.

1.1 Professional software development

1.2 Software engineering ethics

1.3 Case studies

CHAPTER 1 INTRODUCTION

We can't run the modern world without software. National infrastructures and utilities are controlled by computer-based systems and most electrical products include a computer and controlling software. Industrial manufacturing and distribution is completely computerized, as is the financial system. Entertainment, including the music industry, computer games, and film and television, is software intensive. Therefore, software engineering is essential for the functioning of national and international societies.

Software systems are abstract and intangible. They are not constrained by the properties of materials, governed by physical laws, or by manufacturing processes. This simplifies software engineering, as there are no natural limits to the potential of software. However, because of the lack of physical constraints, software systems can quickly become extremely complex, difficult to understand, and expensive to change.

1. Increasing demands 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. Existing software engineering methods cannot cope and new software engineering techniques have to be developed to meet these new demands.

2. Low expectations It is relatively 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. We need better software engineering education and training to address this problem.

Software engineers can be rightly proud of their achievements. Of course we still have problems developing complex software but, without software engineering, we would not have explored space, would not have the Internet or modern telecommunications. All forms of travel would be more dangerous and expensive. Software engineering has contributed a great deal and I am convinced that its contributions in the 21st century will be even greater.

1.1 PROFESSIONAL SOFTWARE DEVELOPMENT

Lots of people write programs. People in business write spreadsheet programs to simplify their jobs, scientists and engineers write programs to process their experimental data, and hobbyists write programs for their own interest and enjoyment. However, the vast majority of software development is a professional activity where software is developed for specific business purposes, for inclusion in other devices, or as software products such as information systems, CAD systems, etc. Professional software, intended for use by someone apart from its developer, is usually developed by teams rather than individuals. It is maintained and changed throughout its life.

Figure 1.1 Frequently asked questions about software

1. Generic products These are stand-alone systems that are produced by a development organization and sold on the open market to any customer who is able to buy them. Examples of this type of product include software for PCs such as databases, word processors, drawing packages, and project-management tools. It also includes so-called vertical applications designed for some specific purpose such as library information systems, accounting systems, or systems for maintaining dental records.

2. Customized (or bespoke) products These are systems that are commissioned by a particular customer. A software contractor develops the software especially for that customer. Examples of this type of software include control systems for electronic devices, systems written to support a particular business process, and air traffic control systems.

An important difference between these types of software is that, in generic products, the organization that develops the software controls the software specification. For custom products, the specification is usually developed and controlled by the organization that is buying the software. The software developers must work to that specification.

However, the distinction between these system product types is becoming increasingly blurred. More and more systems are now being built with a generic product as a base, which is then adapted to suit the requirements of a customer. Enterprise Resource Planning (ERP) systems, such as the SAP system, are the best examples of this approach. Here, a large and complex system is adapted for a company by incorporating information about business rules and processes, reports required, and so on.

1.1.1 Software Engineering

Software engineering is an engineering discipline that is concerned with all aspects of software production from the early stages of system specification through to maintaining the system after it has gone into use. In this definition, there are two key phrases:

1. Engineering discipline Engineers make things work. They apply theories, methods, and tools where these are appropriate. However, they use them selectively and always try to discover solutions to problems even when there are no applicable theories and methods. Engineers also recognize that they must work to organizational and financial constraints so they look for solutions within these constraints.

Figure 1.2 Essential attributes of good software

2. All aspects of software production Software engineering is not just concerned with the technical processes of software development. It also includes activities such as software project management and the development of tools, methods, and theories to support software production. Engineering is about getting results of the required quality within the schedule and budget. This often involves making compromises—engineers cannot be perfectionists. People writing programs for themselves, however, can spend as much time as they wish on the program development. In general, software engineers adopt a systematic and organized approach to their work, as this is often the most effective way to produce high-quality software. However, engineering is all about selecting the most appropriate method for a set of circumstances so a more creative, less formal approach to development may be effective in some circumstances. Less formal development is particularly appropriate for the development of web-based systems, which requires a blend of software and graphical design skills.

Software engineering is important for two reasons: 1. 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. 2. 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 systems, the majority of costs are the costs of changing the software after it has gone into use.

The systematic approach that is used in software engineering is sometimes called a software process. A software process is a sequence of activities that leads to the production of a software product. There are four fundamental activities that are common to all software processes. These activities are: 1. Software specification, where customers and engineers define the software that is to be produced and the constraints on its operation. 2. Software development, where the software is designed and programmed. 3. Software validation, where the software is checked to ensure that it is what the customer requires. 4. Software evolution, where the software is modified to reflect changing customer and market requirements.

Different types of systems need different development processes. For example, real-time software in an aircraft has to be completely specified before development begins. In e-commerce systems, the specification and the program are usually developed together. Consequently, these generic activities may be organized in different ways and described at different levels of detail depending on the type of software being developed. I describe software processes in more detail in Chapter 2.

1.1.2 Software engineering diversity

Software engineering is a systematic approach to the production of software that takes into account practical cost, schedule, and dependability issues, as well as the needs of software customers and producers. How this systematic approach is actually implemented varies dramatically depending on the organization developing the software, the type of software, and the people involved in the development process.

There are many different types of application including:

1. Stand-alone applications These are application systems that run on a local computer, such as a PC. They include all necessary functionality and do not need to be connected to a network.

2. Interactive transaction-based applications These are applications that execute on a remote computer and that are accessed by users from their own PCs or terminals.

3. Embedded control systems These are software control systems that control and manage hardware devices.

4. Batch processing systems These are business systems that are designed to process data in large batches.

5. Entertainment systems These are systems that are primarily for personal use and which are intended to entertain the user.

6. Systems for modeling and simulation These are systems that are developed by scientists and engineers to model physical processes or situations.

7. Data collection systems These are systems that collect data from their environment using a set of sensors.

8. Systems of systems These are systems that are composed of a number of other software systems.

1.1.3 Software engineering and the Web

The development of the World Wide Web has had a profound effect on all of our lives. Initially, the Web was primarily a universally accessible information store and it had little effect on software systems. These systems ran on local computers and were only accessible from within an organization. Around 2000, the Web started to evolve and more and more functionality was added to browsers. This meant that web-based systems could be developed where, instead of a special-purpose user interface, these systems could be accessed using a web browser.

1.2 SOFTWARE ENGINEERING ETHICS

Like other engineering disciplines, software engineering is carried out within a social and legal framework that limits the freedom of people working in that area. As a software engineer, you must accept that your job involves wider responsibilities than simply the application of technical skills. You must also behave in an ethical and morally responsible way if you are to be respected as a professional engineer.

1. Confidentiality You should normally respect the confidentiality of your employers or clients irrespective of whether or not a formal confidentiality agreement has been signed.

2. Competence You should not misrepresent your level of competence. You should not knowingly accept work that is outside your competence.

3. Intellectual property rights You should be aware of local laws governing the use of intellectual property such as patents and copyright. You should be careful to ensure that the intellectual property of employers and clients is protected.

4. Computer misuse You should not use your technical skills to misuse other people's computers. Computer misuse ranges from relatively trivial (game playing on an employer's machine, say) to extremely serious (dissemination of viruses or other malware).

Figure 1.3 The ACM/IEEE Code of Ethics (© IEEE/ACM1999)

Professional societies and institutions have an important role to play in setting ethical standards. Organizations such as the ACM, the IEEE (Institute of Electrical and Electronic Engineers), and the British Computer Society publish a code of professional conduct or code of ethics. Members of these organizations undertake to follow that code when they sign up for membership. These codes of conduct are generally concerned with fundamental ethical behavior.

The Code contains eight Principles related to the behaviour of and decisions made by professional software engineers, including practitioners, educators, managers, supervisors and policy makers, as well as trainees and students of the profession. The Principles identify the ethically responsible relationships in which individuals, groups, and organizations participate and the primary obligations within these relationships.

1.3 CASE STUDIES

To illustrate software engineering concepts, I use examples from three different types of systems throughout the book. The reason why I have not used a single case study is that one of the key messages in this book is that software engineering practice depends on the type of systems being produced. I therefore choose an appropriate example when discussing concepts such as safety and dependability, system modeling, reuse, etc.

The three types of systems that I use as case studies are:

1. An embedded system This is a system where the software controls a hardware device and is embedded in that device. Issues in embedded systems typically include physical size, responsiveness, power management, etc. The example of an embedded system that I use is a software system to control a medical device.

2. An information system This is a system whose primary purpose is to manage and provide access to a database of information. Issues in information systems include security, usability, privacy, and maintaining data integrity. The example of an information system that I use is a medical records system.

3. A sensor-based data collection system This is a system whose primary purpose is to collect data from a set of sensors and process that data in some way. The key requirements of such systems are reliability, even in hostile environmental conditions, and maintainability. The example of a data collection system that I use is a wilderness weather station.

I introduce each of these systems in this chapter, with more information about each of them available on the Web.

1.3.1 An insulin pump control system

An insulin pump is a medical system designed to mimic the pancreas by automatically delivering insulin to diabetic patients. Traditional treatment requires manual measurement of blood sugar and insulin injections, which can lead to risks of dangerously low or high glucose levels. Low glucose can cause brain malfunction, unconsciousness, or death, while prolonged high glucose can damage organs. Advances in miniaturized sensors now allow automated systems that continuously monitor blood sugar and deliver precise insulin doses.

Clearly, this is a safety-critical system. If the pump fails to operate or does not operate correctly, then the user's health may be damaged or they may fall into a coma because their blood sugar levels are too high or too low.

There are, therefore, two essential high-level requirements that this system must meet: 1. The system shall be available to deliver insulin when required. 2. The system shall perform reliably and deliver the correct amount of insulin to counteract the current level of blood sugar.

1.3.2 A patient information system for mental health care

A patient information system to support mental health care is a medical information system that maintains information about patients suffering from mental health problems and the treatments that they have received. Most mental health patients do not require dedicated hospital treatment but need to attend specialist clinics regularly where they can meet a doctor who has detailed knowledge of their problems. The MHC-PMS (Mental Health Care-Patient Management System) is an information system that is intended for use in clinics. It makes use of a centralized database of patient information but has also been designed to run on a PC, so that it may be accessed and used from sites that do not have secure network connectivity.

The MHC-PMS has two overall goals:

1. To generate management information that allows health service managers to assess performance against local and government targets. 2. To provide medical staff with timely information to support the treatment of patients.

1.3.3 A wilderness weather station

To help monitor climate change and to improve the accuracy of weather forecasts in remote areas, the government of a country with large areas of wilderness decides to deploy several hundred weather stations in remote areas. These weather stations collect data from a set of instruments that measure temperature and pressure, sunshine, rainfall, wind speed, and wind direction.

Wilderness weather stations are part of a larger system, which is a weather information system that collects data from weather stations and makes it available to other systems for processing.

The systems include:

1. The weather station system This is responsible for collecting weather data, carrying out some initial data processing, and transmitting it to the data management system.

2. The data management and archiving system This system collects the data from all of the wilderness weather stations, carries out data processing and analysis.

3. The station maintenance system This system can communicate by satellite with all wilderness weather stations to monitor the health of these systems.

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