Introduction to Software Engineering PDF

CS281 Introduction to Software Engineering Courtesy: Dr. Abdulmajeed Aljuhani Source: adapted from Ian Sommerville's lecture notes: SE9 1  Software Products Generic products Stand-al...

CS281 Introduction to Software Engineering Courtesy: Dr. Abdulmajeed Aljuhani Source: adapted from Ian Sommerville's lecture notes: SE9 1  Software Products Generic products Stand-alone systems that are marketed and sold to any customer who wishes to buy them. Examples: graphics programs, project management tools, CAD software, ….etc. 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 Software that is commissioned by a specific customer to meet their own needs. Examples : embedded control systems, air traffic control software,….etc. The specification of what the software should do is owned by the customer and they make decisions on software changes that are required. Source: adapted from Ian Sommerville's lecture notes: SE9 2  Software Costs Software costs often dominate computer system costs. Software costs more to maintain than it does to develop. For systems with a long life, maintenance costs may be several times development costs. Source: adapted from Ian Sommerville's lecture notes: SE9 Importance of S/W 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. For most types of system, the majority of costs are the costs of changing the software after it has gone into use. Source: adapted from Ian Sommerville's lecture notes: SE9 4  Software Engineering is an engineering discipline that is….. Concerned with theories, methods and tools for professional and cost-effective software development. 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. i.e. Not just technical process of development. Also project management and the development of tools, methods etc. to support software production. Source: adapted from Ian Sommerville's lecture notes: SE9  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 Good software should deliver the required functionality and software? 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 Computer science focuses on theory and fundamentals; software engineering and software engineering is concerned with the practicalities of computer science? developing and delivering useful software. What is the difference between System engineering is concerned with all aspects of software engineering and system computer-based systems development including hardware, engineering? software and process engineering. Software engineering is part of this more general process. Source: adapted from Ian Sommerville's lecture notes: SE9 6 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 including security 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. Source: adapted from Ian Sommerville's lecture notes: SE9 7  Software Process Activities S/W specification, where customers and engineers define the software that is to be produced and the constraints on its operation. S/W development, where the software is designed and programmed. S/W validation, where the software is checked to ensure that it is what the customer requires. S/W evolution, where the software is modified to reflect changing customer and market requirements. Source: adapted from Ian Sommerville's lecture notes: SE9 8  Software Engineering Diversity There are many different types of software systems and there is no universal set of software techniques that is applicable to all of these. As such, the software engineering methods and tools used depend on: 1) the type of application being developed, 2) the requirements of the customer, and 3) the background of the development team. However, some fundamental principles apply to all types of software systems, irrespective of the development techniques used. See next slide! Source: adapted from Ian Sommerville's lecture notes: SE9 9  S/W Engineering Fundamentals Some fundamental principles apply to all types of software systems, irrespective of the development techniques used: 1. Systems should be developed using a managed and understood development process. Of course, different processes are used for different types of software. 2. Dependability and performance are important for all types of system. 3. Understanding and managing the software specification and requirements (what the software should do) are important. 4. Where appropriate, you should reuse software that has already been developed rather than write new software. Source: adapted from Ian Sommerville's lecture notes: SE9 10 Application Types Another classification.. Stand-alone applications. Run on a local computer and include all necessary functionality. They do not need to be connected to a network. Interactive transaction-based applications Execute on a remote computer and are accessed by users from their own PCs or terminals (e. g. Web applications, such as E-commerce applications. Embedded control systems S/W systems that control and manage hardware devices. Data collection systems Systems that collect data from their environment using a set of sensors and send that data to other systems for processing. Source: adapted from Ian Sommerville's lecture notes: SE9 11  Application Types – Cont. 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 Primarily for personal use and are intended to entertain the user. Systems for modeling and simulation Developed by scientists and engineers to model physical processes or situations, which include many, separate, interacting objects. Systems of systems These are systems that are composed of a number of other software systems. Source: adapted from Ian Sommerville's lecture notes: SE9 12  Software Engineering &The Web The Web is now a platform for running applications, and organizations are increasingly developing web-based systems rather than local systems. Web services* 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, but rather pay according to their use. * For more information about Web Services see Chapter 19 in the text book Source: adapted from Ian Sommerville's lecture notes: SE9 13  Web-Based S/W Engineering 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. Web-based systems should be developed and delivered incrementally. Web-based systems are usually complex distributed systems and it is now generally recognized that it is impractical to specify all the requirements for such systems in advance. User interfaces are constrained by the capabilities of web browsers. Technologies such as AJAX allow rich interfaces to be created within a web browser but are still difficult to use. Web forms with local scripting are more commonly used. Source: adapted from Ian Sommerville's lecture notes: SE9 14  General Issues Affecting Most 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. Security and trust As software is intertwined with all aspects of our lives, it is essential that we can trust that software. Source: adapted from Ian Sommerville's lecture notes: SE9 15  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. Source: adapted from Ian Sommerville's lecture notes: SE9  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. Source: adapted from Ian Sommerville's lecture notes: SE9  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). Source: adapted from Ian Sommerville's lecture notes: SE9  So far…. We continued with the introduction to software engineering and professional software development. Particularly: Attributes of good software Software process activities Software engineering fundamentals Software engineering diversity and application types Software engineering and the Web General issues that affect most software Software engineering ethics Source: adapted from Ian Sommerville's lecture notes: SE9 19  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 fundamental principles and ideas of software engineering are universally applicable to all types of system development. There are many different types of system and each requires appropriate software engineering tools and techniques for their development. Source: adapted from Ian Sommerville's lecture notes: SE9 20  Next lecture... We well have a look at the “Software Processes”. Source: adapted from Ian Sommerville's lecture notes: SE9 21