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What is software Engineering?

Software engineering (SE) is concerned with developing and maintaining software systems that behave reliably and efficiently, are affordable to develop and maintain, and satisfy all the requirements that customers have defined for them. It is important because of the impact of large, expensive software systems and the role of software in safety-critical applications. It integrates significant mathematics, computer science and practices whose origins are in engineering.

Since the dawn of computing in the 1940s, the applications and uses of computers have grown at a staggering rate. Software plays a central role in almost all aspects of daily life: in government, banking and finance, education, transportation, entertainment, medicine, agriculture, and law. The number, size, and application domains of computer programs have grown dramatically; as a result, hundreds of billions are being spent on software development, and the livelihood and lives of most people depend on the effectiveness of this development. Software products have helped us to be more efficient and productive. They make us more effective problem solvers, and they provide us with an environment for work and play that is often safer, more flexible, and less confining. Despite these successes, there are serious problems in the cost, timeliness, and quality of many software products.

The reasons for these problems are many and include the following:

Software products are among the most complex of man-made systems, and software by its  very nature has intrinsic, essential properties (e.g., complexity, invisibility, and changeability) that are not easily addressed.
Programming techniques and processes that worked effectively for an individual or a small team to develop modest-sized programs do not scale-up well to the development of large, complex systems (i.e., systems with millions of lines of code, requiring years of work, by hundreds of software developers).
The pace of change in computer and software technology drives the demand for new and evolved software products. This situation has created customer expectations and competitive forces that strain our ability to produce quality of software within acceptable development schedules.

It has been over thirty-five years since the first organized, formal discussion of software engineering as a discipline took place at the 1968 NATO Conference on Software Engineering [Naur 1969]. The term “software engineering” is now widely used in industry, government, and academia: hundreds of thousands of computing professionals go by the title “software engineer”; numerous publications, groups and organizations, and professional conferences use the term software engineering in their names; and there are many educational courses and programs on software engineering. However, there are still disagreements and differences of opinion about the meaning of the term. The following definitions provide several views of the meaning and nature of software engineering. Nevertheless, they all possess a common thread, which states, or strongly implies that software engineering is more than just coding – it includes quality, schedule and economics, and the knowledge and application of principles and discipline.
Software is often found in products and situations where very high reliability is expected, even under demanding conditions, such as monitoring and controlling nuclear power plants, or keeping a modern airliner aloft. Such applications contain millions of lines of code, making them comparable in complexity to the most complex modern machines. For example, a modern airliner has several million physical parts (and the space shuttle about ten million parts), while the software for such an airliner can run to 4 million lines of code.

Definitions of Software Engineering

Over the years, numerous definitions of the discipline of Software Engineering have been presented. For the purpose of this document, we highlight the following definitions:

“The establishment and use of sound engineering principles (methods) in order to obtain   economically software that is reliable and works on real machines” [Bauer 1972].
“Software engineering is that form of engineering that applies the principles of computer science and mathematics to achieving cost-effective solutions to software problems.” [CMU/SEI-90-TR-003] “The application of a systematic, disciplined, quantifiable approach to the development, operation, and maintenance of software” [IEEE 1990].

There are aspects of each of these definitions that contribute to the perspective of software engineering used in the construction of this volume. One particularly important aspect is that software engineering builds on computer science and mathematics. But, in the engineering tradition, it goes beyond this technical basis to draw upon a broader range of disciplines.