Software Engineering Lecture Notes 1 PDF

Chapter 1- Introduction 30/10/2014 Chapter 1 Introduction 1 Topics covered ✧ Professional software development ▪ What is meant by software engineering. ✧ Software engineering ethics ▪ A brief introduction to ethical issues that affect software engineering. ✧ Cas...

Chapter 1- Introduction 30/10/2014 Chapter 1 Introduction 1 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. 30/10/2014 Chapter 1 Introduction 2 Software engineering ✧ The economies of ALL developed nations are dependent on software. ✧ More and more systems are software controlled ✧ Software engineering is concerned with theories, methods and tools for professional software development. ✧ Expenditure on software represents a significant fraction of GNP in all developed countries. 30/10/2014 Chapter 1 Introduction 3 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. 30/10/2014 Chapter 1 Introduction 4 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. 30/10/2014 Chapter 1 Introduction 5  Professional software development 30/10/2014 Chapter 1 Introduction 6 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 Software specification, software development, software engineering activities? validation and software evolution. What is the difference between software Computer science focuses on theory and fundamentals; engineering and computer science? software engineering is concerned with the practicalities of developing and delivering useful software. What is the difference between software System engineering is concerned with all aspects of engineering and system engineering? computer-based systems development including hardware, software and process engineering. Software engineering is part of this more general process. 30/10/2014 Chapter 1 Introduction 7 Frequently asked questions about software engineering Question Answer What are the key challenges facing Coping with increasing diversity, demands for reduced software engineering? delivery times and developing trustworthy software. What are the costs of software Roughly 60% of software costs are development costs, engineering? 40% are testing costs. For custom software, evolution costs often exceed development costs. What are the best software engineering While all software projects have to be professionally techniques and methods? 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 The web has led to the availability of software services software engineering? 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. 30/10/2014 Chapter 1 Introduction 8 Software products ✧ Generic products ▪ Stand-alone systems that are marketed and sold to any customer who wishes to buy them. ▪ Examples – PC software such as graphics programs, project management tools; CAD software; software for specific markets such as appointments systems for dentists. ✧ Customized products ▪ Software that is commissioned by a specific customer to meet their own needs. ▪ Examples – embedded control systems, air traffic control software, traffic monitoring systems. 30/10/2014 Chapter 1 Introduction 9 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. 30/10/2014 Chapter 1 Introduction 10 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 Software dependability includes a range of characteristics security 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. 30/10/2014 Chapter 1 Introduction 11 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. ✧ Engineering discipline ▪ Using appropriate theories and methods to solve problems bearing in mind organizational and financial constraints. ✧ All aspects of software production ▪ Not just technical process of development. Also project management and the development of tools, methods etc. to support software production. 30/10/2014 Chapter 1 Introduction 12 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. 30/10/2014 Chapter 1 Introduction 13 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. 30/10/2014 Chapter 1 Introduction 14 General issues that affect software ✧ Heterogeneity ▪ Increasingly, systems are required to operate as distributed systems across networks that include different types of computer and mobile devices. ✧ Business and social change ▪ Business and society are changing incredibly quickly as emerging economies develop and new technologies become available. They need to be able to change their existing software and to rapidly develop new software. 30/10/2014 Chapter 1 Introduction 15 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. 30/10/2014 Chapter 1 Introduction 16 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. 30/10/2014 Chapter 1 Introduction 17 Application types ✧ 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. ✧ Interactive transaction-based applications ▪ Applications that execute on a remote computer and are accessed by users from their own PCs or terminals. These include web applications such as e-commerce applications. ✧ Embedded control systems ▪ These are software control systems that control and manage hardware devices. Numerically, there are probably more embedded systems than any other type of system. 30/10/2014 Chapter 1 Introduction 18 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. ✧ Entertainment systems ▪ These are systems that are primarily for personal use and which are intended to entertain the user. ✧ 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. 30/10/2014 Chapter 1 Introduction 19 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. ✧ Systems of systems ▪ These are systems that are composed of a number of other software systems. 30/10/2014 Chapter 1 Introduction 20 Software engineering fundamentals ✧ Some fundamental principles apply to all types of software system, irrespective of the development techniques used: ▪ Systems should be developed using a managed and understood development process. Of course, different processes are used for different types of software. ▪ Dependability and performance are important for all types of system. ▪ Understanding and managing the software specification and requirements (what the software should do) are important. ▪ Where appropriate, you should reuse software that has already been developed rather than write new software. 30/10/2014 Chapter 1 Introduction 21 Internet software engineering ✧ The Web is now a platform for running application and organizations are increasingly developing web-based systems rather than local systems. ✧ Web services (discussed in Chapter 19) allow application functionality to be accessed over the web. ✧ Cloud computing is an approach to the provision of computer services where applications run remotely on the ‘cloud’. ▪ Users do not buy software buy pay according to use. 30/10/2014 Chapter 1 Introduction 22 Web-based software engineering ✧ Web-based systems are complex distributed systems but the fundamental principles of software engineering discussed previously are as applicable to them as they are to any other types of system. ✧ The fundamental ideas of software engineering apply to web-based software in the same way that they apply to other types of software system. 30/10/2014 Chapter 1 Introduction 23  Web software engineering ✧ Software reuse ▪ Software reuse is the dominant approach for constructing web-based systems. When building these systems, you think about how you can assemble them from pre-existing software components and systems. ✧ Incremental and agile development ▪ Web-based systems should be developed and delivered incrementally. It is now generally recognized that it is impractical to specify all the requirements for such systems in advance. 30/10/2014 Chapter 1 Introduction 24 Web software engineering ✧ Service-oriented systems ▪ Software may be implemented using service-oriented software engineering, where the software components are stand-alone web services. ✧ Rich interfaces ▪ Interface development technologies such as AJAX and HTML5 have emerged that support the creation of rich interfaces within a web browser. 30/10/2014 Chapter 1 Introduction 25  Software engineering ethics 30/10/2014 Chapter 1 Introduction 26 Software engineering ethics ✧ Software engineering involves wider responsibilities than simply the application of technical skills. ✧ Software engineers must behave in an honest and ethically responsible way if they are to be respected as professionals. ✧ Ethical behaviour is more than simply upholding the law but involves following a set of principles that are morally correct. 30/10/2014 Chapter 1 Introduction 27 Issues of professional responsibility ✧ Confidentiality ▪ Engineers should normally respect the confidentiality of their employers or clients irrespective of whether or not a formal confidentiality agreement has been signed. ✧ Competence ▪ Engineers should not misrepresent their level of competence. They should not knowingly accept work which is outwith their competence. 30/10/2014 Chapter 1 Introduction 28 Issues of professional responsibility ✧ Intellectual property rights ▪ Engineers should be aware of local laws governing the use of intellectual property such as patents, copyright, etc. They should be careful to ensure that the intellectual property of employers and clients is protected. ✧ Computer misuse ▪ Software engineers should not use their 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). 30/10/2014 Chapter 1 Introduction 29 ACM/IEEE Code of Ethics ✧ The professional societies in the US have cooperated to produce a code of ethical practice. ✧ Members of these organisations sign up to the code of practice when they join. ✧ 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. 30/10/2014 Chapter 1 Introduction 30 Rationale for the code of ethics ▪ Computers have a central and growing role in commerce, industry, government, medicine, education, entertainment and society at large. Software engineers are those who contribute by direct participation or by teaching, to the analysis, specification, design, development, certification, maintenance and testing of software systems. ▪ Because of their roles in developing software systems, software engineers have significant opportunities to do good or cause harm, to enable others to do good or cause harm, or to influence others to do good or cause harm. To ensure, as much as possible, that their efforts will be used for good, software engineers must commit themselves to making software engineering a beneficial and respected profession. 30/10/2014 Chapter 1 Introduction 31 The ACM/IEEE Code of Ethics Software Engineering Code of Ethics and Professional Practice ACM/IEEE-CS Joint Task Force on Software Engineering Ethics and Professional Practices PREAMBLE The short version of the code summarizes aspirations at a high level of the abstraction; the clauses that are included in the full version give examples and details of how these aspirations change the way we act as software engineering professionals. Without the aspirations, the details can become legalistic and tedious; without the details, the aspirations can become high sounding but empty; together, the aspirations and the details form a cohesive code. Software engineers shall commit themselves to making the analysis, specification, design, development, testing and maintenance of software a beneficial and respected profession. In accordance with their commitment to the health, safety and welfare of the public, software engineers shall adhere to the following Eight Principles: 30/10/2014 Chapter 1 Introduction 32 Ethical principles 1. PUBLIC - Software engineers shall act consistently with the public interest. 2. CLIENT AND EMPLOYER - Software engineers shall act in a manner that is in the best interests of their client and employer consistent with the public interest. 3. PRODUCT - Software engineers shall ensure that their products and related modifications meet the highest professional standards possible. 4. JUDGMENT - Software engineers shall maintain integrity and independence in their professional judgment. 5. MANAGEMENT - Software engineering managers and leaders shall subscribe to and promote an ethical approach to the management of software development and maintenance. 6. PROFESSION - Software engineers shall advance the integrity and reputation of the profession consistent with the public interest. 7. COLLEAGUES - Software engineers shall be fair to and supportive of their colleagues. 8. SELF - Software engineers shall participate in lifelong learning regarding the practice of their profession and shall promote an ethical approach to the practice of the profession. 30/10/2014 Chapter 1 Introduction 33 Key points ✧ Software engineering is an engineering discipline that is concerned with all aspects of software production. ✧ Essential software product attributes are maintainability, dependability and security, efficiency and acceptability. ✧ The high-level activities of specification, development, validation and evolution are part of all software processes. ✧ The fundamental notions of software engineering are universally applicable to all types of system development. 30/10/2014 Chapter 1 Introduction 34 Key points ✧ There are many different types of system and each requires appropriate software engineering tools and techniques for their development. ✧ The fundamental ideas of software engineering are applicable to all types of software system. ✧ Software engineers have responsibilities to the engineering profession and society. They should not simply be concerned with technical issues. ✧ Professional societies publish codes of conduct which set out the standards of behaviour expected of their members. 30/10/2014 Chapter 1 Introduction 35