Software development

Software engineering technologies and practices help developers to create and maintain applications, while maximizing productivity and quality. Today, these diverse technologies and practices include languages, databases, tools, platforms, libraries, standards, patterns, and processes.

Software engineering applications embody social and economic value, in that they make people more productive, improve their quality of life, and enable them to do things that would otherwise be impossible. Today, these diverse applications include banking, compilers, databases, email, embedded software, graphics, office suites, operating systems, robotics, video games, and the world wide web.

Software engineering today

Software engineering is alive and well today.

Importance of software engineering

In the USA, software drove about 1/4 of all increase in GDP during the 1990s (about $90 billion per year), and 1/6 of all productivity growth (efficiency within GDP) during the late 1990s (about $33 billion per year).

Software engineering has changed the world's culture, wherever people use computers. Email, the world-wide web, and instant messaging enable people to interact in new ways. Software lowers the cost of many important social goods and services, such as health-care and fire departments.

Examples of successful large projects, where software engineering methods have been applied, include Linux, the space shuttle software, and automated teller machines. When it is cheaper to run a business with software applications than without, businesses often invest in computer hardware, software, and personnel.

Today's Practice

Practitioners specialize in many roles in industry (analysts, developers, testers, managers) and academe (educators, researchers).

Most software engineers work for others as employees or contractors. Software engineers may work with a profit-seeking corporation (a business), a government (civilian or military), or a non-profit agency such as a school or .org, such as Wikipedia. Some software engineers work for themselves as free agents.

Software engineers are part of a much larger software, hardware, application, and operations community. In the U.S. there are about 680,000 software engineers and about 10,000,000 IT workers.

Today's Education

About half of software engineers today have computer science degrees. Many others have science, engineering, or other technical degrees. Some have business, or other non-technical degrees. And, some have no degrees.

Graduate software engineering degrees have been available from dozens of universities for a decade or so. New undergraduate software engineering degrees are being established at many universities, today. But only a small fraction of schools that offer computer science degrees also offer software engineering degrees. So, most practitioners still earn computer science degrees, even though someday more will earn software engineering degrees.

A new international curriculum for software engineering is currently being defined by the CCSE.

Current directions for software engineering

Agile processes are important emerging practices. Aspect programming is also an important emerging technology.

Agile processes are methods to manage software development so projects evolve with changing expectations. The older document-driven processes (like CMM and ISO 9000) may be fading in importance. Some people believe that companies have exported many of the jobs that can be controlled by older processes. Related concepts are Lean software development and Extreme programming.

Aspects help programmers deal with ilities by providing tools to add or remove boilerplate code from many areas in a software project. Aspects describe how all objects or functions should behave in a particular circumstance. For example, aspects can add debugging, logging, or locking control into all objects of a particular type. Related concepts are Generative programming and Templates.

The future of software engineering was an important conference at the ICSE 2000, [1]. The FOSE project summarized the state of the art in 2000 and listed many problems to be solved over the next decade. The Feyerabend project is attempting to discover the future, [2].

Evolution

Software engineering has evolved steadily from its founding days in the 1940s until today in the 2000s. There has been a continuity of practice. The ongoing goal has been to improve technologies and practices, the productivity of practitioners, and the quality of applications.

1945 to 1965: The origins

The term software engineering first was used in the late 1950s and early 1960s. Programmers were well aware of civil, electrical, and computer engineering and debated what engineering might mean for software.

The NATO Science Committee sponsored two conferences on software engineering in 1968 (Garmisch, Germany) and 1969, which gave the field its initial boost. Many believe these conferences mark the start of the profession.

1965 to 1985: The software crisis

Software engineering was spurred by the so-called software crisis of the 1960s, 1970s, and 1980s. The software crisis was the name that identified the many problems of software development with the many software projects that ended badly. Many software projects ran over budget and schedule. Some projects caused property damage. A few projects caused loss of life. Some companies used the term to refer to their inability to hire qualified personnel. The software crisis was originally defined in terms of productivity, but evolved to emphasize quality.

Cost and Budget Overruns: The OS 360 operating system was a classic example. It is still used on the IBM 360 Series and its descendants. This decade-long project eventually produced a working system amongst the most complex software systems ever designed. OS 360 was one of the first very large (1000 programmer) software projects. Fred Brooks admits in Mythical Man Month that he made a multi-million dollar mistake when he managed the project.

According to a study by the Standish Group, in 2000, only 28 percent of software projects could be classed as complete successes (meaning they were executed on time and on budget), while 23 percent failed outright. Many projects were abandoned.

Property Damage: Software defects can cause property damage. Poor software security allows hackers to steal identities, costing time, money and reputations. The explosion of a European Ariane rocket and other disasters spurred further developments in the field.

Life and Death: Defects in software have killed. Several embedded systems used in radiotherapy machines failed so catastrophically that they administered lethal doses of radiation to patients.

A large list of contemporary software problems and disasters is kept at Peter G. Neumann's Computer Risks column.

1985 to present: No silver bullet

For decades, solving the software crisis was paramount to researchers. Seemingly, every new technology and practice from the 1970s to the 1990s was trumpeted as a silver bullet to solve the software crisis.

Technologies: Every new technology and practice for decades was touted as the solution to the software crisis: structured programming, object-oriented programming, process, CMM, UML, Ada, methodologies, and so on. Especially emphasised were tools, such as CASE tools, Ada, and so on.

Practices: Some pundits argued that the software crisis was due to the lack of discipline of programmers. Formal methods: Some believed that if formal engineering methodologies could be applied to software development, the production of software would become as predictable an industry as other branches of engineering. Process: Many advocated process. Professionalism: This led to work on a code of ethics, and professionalism.

In 1987, Brooks published the famous paper "No Silver Bullet", arguing that no individual technology or practice would make a 10-fold improvement in productivity in 10 years.

Debate about silver bullets raged over the following decade. Some advocates for particular technologies continued to argue that their favorite technology or practice would be the silver bullet. Sceptics disagreed. But eventually, almost everyone accepted that no silver bullets would ever be found. Yet, the term silver bullet pops up now and again in marketing, even today.

All known useful technologies and practices have made incremental improvements in productivity and quality.

Major developments

Process and methodology

See also software development process and methodology. Many practitioners resist process strongly.

Emergence as a profession

In the mid-1990s to mid-2000s, software engineering emerged as a bona fide profession, to stand beside computer science and traditional engineering.

Prior to the mid-1990s, most software practitioners called themselves programmers or developers, regardless of their actual jobs.

The term programmer had often been used as a pejorative term to refer to those who lacked the skills, education, or ethics to write quality software. Practitioners began to describe themselves as software engineers to escape the stigma attached to programmer. In many companies, the titles "programmer" and "software developer" were changed to "software engineer", for many categories of programmers.

This caused confusion, because some denied any difference while others tried to create a difference. Traditional engineers questioned whether software engineers could legally use the term.

See also Software engineering professionalism.

Role of women

In the 1940s, 1950s, and 1960s, software was a women's ghetto. Men preferred the higher prestige of hardware engineering roles. So, women filled the programming roles. Women like Grace Hopper were common.

Many unsung women wrote code prior to 1968. Today, relatively few women work in software engineering. Women have largely moved into analysis and testing roles. Saying that this is sexual discrimination is too simple, because it related directly to individual identity. In this sense, software engineering is the masculinization of programming.

The role women play continues to evolve. Today, women in software engineering frequently do analysis, testing, education, documentation, and management, rather than hard-core development.

Ada Lovelace was deeply in debt, and was attracted to Babbage's scheme so that she could gamble on horses more effectively.

Other

The relative cost of software versus hardware has changed substantially. When mainframes were expensive, software projects could be expensive. Because powerful PCs are cheap, software costs must become cheaper, in comparison.

Comparing Related Fields

The relationship between software engineering and the related fields of programming, computer science, and traditional engineering has been debated for many decades. Many of the similarities and differences are discussed here.

Whether software development is more like art, science or engineering has been fiercely debated for many decades. Software development shares attributes of all of these fields, and many software projects have elements of all, but important distinctions exist.

Comparing programming

Programmers emphasize the task of writing code to produce working software applications, independent of budget and schedule.

Software engineers work on all sizes of applications: small and large.

Software engineering tries to encompass software projects more completely, including budget and schedule. Software engineering recognizes that software development fits in a large business context with relationships to marketing, sales, production, installation, training, support, and operations. Software engineering emphasizes methods to construct large applications that individual programmers cannot write alone. Software engineers strive to write applications in a consistent way.

Issue	Software Engineering	Programming
Scope	Relates development to final product.	Emphasizes programming.
Team size	Individuals to large teams.	Emphasizes individual efforts.
Number of Practitioners in U.S.	680,000	530,000

Comparing computer science

Many believe that (metaphorically) software engineering is to computer science and information science as traditional engineering is to physics and chemistry.

While about half of all software engineers earn computer science degrees, they practice software engineering (developing applications) every day, which differs significantly from practicing computer science (doing theory) every day.

Issue	Software Engineering	Computer Science
Ideal	Constructing software applications for real-world use	Correct eternal truths about computability and algorithms with good runtime behavior
Goals	Working programs (like office suites and compilers)	Algorithms (like Shell sort) and abstract problems (like travelling salesman problem)
Budgets and Schedules	Projects (like the next upgrade) have fixed budgets and schedules.	Projects (like solving NP) are independent of budget and schedule.
Emphasis	Software engineering emphasizes applying skills and working programs that deliver value to users.	Computer science emphasizes eternal truths, like the running time analysis, space analysis, and correctness of algorithms.
Change	Programs will evolve as user needs and expectations evolve, and as SE technologies and practices evolve.	When computer science problems are solved, the solution will never change.
Additional Skills	Domain knowledge	Mathematics
Notable Educators and Researchers	Barry Boehm, Frederick P. Brooks, and David Parnas	Edsger Dijkstra, Donald Knuth, Robert Tarjan, and Alan Turing
Notable Practitioners	John Backus, Dan Bricklin, Tim Berners-Lee, Linus Torvalds, Richard Stallman	Not applicable
Number of Practitioners in U.S.	640,000	25,000
Number of Practitioners in World	unknown	unknown

Comparing traditional engineering

Some people believe that SEs apply concepts from traditional engineering to software development. They believe engineering provides a structured, logical approach, and therefore, a stable final product. Other practitioners are inspired by traditional engineering, but believe that software problems need particular solutions. They believe that traditional engineering concepts may not apply, because software is fundamentally different than bridges and roads. For example, traditional engineers do not use compilers or linkers to build roads.

Software engineers aspire to build low-cost, reliable, safe software, which is much like what traditional engineers do.

Software engineers borrow many metaphors and techniques from traditional engineering disciplines: requirements analysis, quality control, and project management techniques.

All engineering fields use software extensively. Traditional engineers use software tools to design and analyze their own systems, such as bridges and buildings. These new kinds of design and analysis resemble programs in many respects, because the work exists as electronic documents and goes through analysis, design, implementation, and testing phases, just like software. When it is cheaper to build a software simulation than to build an engineering model, traditional engineers usually build the simulation. Many traditional engineers write software as part of their own products. Software is part of the control systems of HVAC systems, airplanes, and automobiles.

Issue	Software Engineering	Traditional Engineering
Foundations	Software engineering is based on computer science, information science, and discrete math.	Traditional engineering is based on physics, chemistry, and calculus.
Cost	Compilers and computers are now cheap, so software engineering and consulting often cost more than 50% of a project. Even minor software engineering cost-overruns can affect the total project cost.	Construction and manufacturing costs are high, so traditional engineering may only cost 15% of a project. Even major engineering cost overruns may not affect a project's viability.
Replication	Replication is trivial, and most development effort goes into building new (unproven) or changing old designs and features.	Most development effort goes into replicating proven designs.
Innovation	Software engineers often apply new and untested elements in software projects.	Though some projects have innovations, traditional engineers apply known and tested principles, and limit the untested innovations that goes into each product.
Management Status	Few software engineers manage anyone, so they are not viewed as managers, except by themselves.	Many traditional engineers manage construction, manufacturing, or maintenance crews, so they are all treated as managers.
Number of Practitioners in U.S. in 2000	640,000	1,100,000 total engineers 65,000 computer engineers
Age	Software engineering is about 50 years old.	Civil engineering is thousands of years old.

In the U.S., there are 10 times as many software engineers as computer engineers, and the software engineering community is about 60% as large as the traditional engineering community.

Differences of Opinion

As software becomes more pervasive, we all recognize the need for better software. Everyone agrees that we want better software. We disagree on priorities and approach, on what an individual should do first in a specific circumstance. Proponents advocate conflicting solutions. Different methodologies advocate different solutions. Proponents of different methodologies often get into heated debates over their merits.

With an industry of 640,000 software engineers and 530,000 programmers in the USA, and many more around the world, there should be room for many approaches. Subfields like consumer applications are sensitive to time and cost. Subfields like military and medical applications are sensitive to quality. All subfields mix these needs to varying degrees. There should be room for people to try different approaches. However a consensus has yet to emerge.

Fighting over words

The term engineering causes a lot of confusion. Some believe that it means that practitioners must be traditional engineers. Others believe that engineering is a metaphor that practitioners apply as appropriate.

Traditional engineers (especially civil engineers) claim that they have a special rights over the term engineering, and for other any field to use the term requires their approval.

The fields of data engineering, knowledge engineering, user interface engineering, and so on have similar concerns over engineering issues.

Many people prefer the term software developer, though some still prefer the term "programmer". Many argue that they all essentially do the same thing with computers.

Some claim that software engineering is already as predicatable and reliable as many fields of engineering, such as space or biological engineering. Although large, reliable software systems can be and have been constructed, software projects that fail during construction or in service are still too common. However, failures in large traditional engineering systems, such as those preceding the disasters in Three Mile Island, Chernobyl, Bhopal Disaster, Space Shuttles Challenger and Columbia are also too common. Others argue that unlike in traditional engineering where practicioners analyze failures, find precise causes, and set up guidelines to avoid them in the future software engineers routinely fail to pinpoint causes of failure or delay precisely enough to avoid repeats in the future.

Fighting over issues

Everyone seems to emphasize a different combination of the following issues.

Management practices: Some argued that software engineering was primarily about the management practices necessary to make budgets and schedules. The Software Engineering Institute took this approach to create the CMM.

Formal methods: Some applied rigorous mathematical analysis to computer programming. The perception at the time was that conventional engineering was carried out with a great degree of mathematical rigor, while computer programming was commonly seen as an iterative trial and error process. It's likely that neither of these perceptions were especially accurate, but the term software engineering was adopted to indicate an intent to make programming more rigorous.

Methodologies: Some have argued that software engineering must follow a step-by-step methodology, much like an assembly line. This inspired many methodologies, such as RUP.

Tools: Many argue that software engineering means tools, especially CASE tools.

Traditional engineering: Many have defined software engineering as a subset of traditional engineering. This means that software engineers should study physics and chemistry.

Ethics: Some argued that software engineering mostly need codes of ethics and social responsibility.

Licenses: Some have defined software engineering in terms of licenses, like traditional engineers have. The biggest advocates of this position are in Texas and Canada, where the state governments sponsor licenses.

Criticisms of software engineering

Critics charge that some assumptions made during the process of implementing software engineering are inherently flawed. However, these criticisms may seem to apply to every human activity (Eg : fine arts or even quantum cryptography). Hence, a few believe that these criticisms do not hold much water. The following paragraphs detail many of the criticisms and some responses to them.

Managing Expectations

Criticism: One key to successful "software engineering" projects is managing the customer's expectations to something that can be built and delivered. So, the field resembles marketing, sociology, or voodoo, more than traditional engineering with its responsibilities to society at large and the perils of legal liability with failure to protect the public interest.

Response: Every profession manages expectations, including all forms of engineering. This may happen at different levels. Software engineering focuses on immediate requirements, whereas other engineering fields tend to solve problems that long-ranged (bridges and dams). Moreover, "responsibility to the society" means meeting the expectations of the general public, which can be considered a customer.

Poor Requirements

Criticism: The requirements for most projects are incomplete or inconsistent. Some customers have little previous experience in writing requirements for a software project. Other customers really do not know what they want, and say "I'll know it when I see it" (IKIWISI). Even experienced customers who know exactly what they want may be unable to articulate their requirements. Users frequently expect far more than they write in specifications. And, complete requirements may describe programs that have no computable or practical solutions.

Response One response to this objection is that one must avoid all unclear projects (but there might be no others left). Another response is agile development and rapid prototyping to clarify project goals as soon as possible. Some branches of software engineering like Embedded systems are unique in that they are designed by other engineers, who can sometimes define interfaces completely.

Rising Complexity

Criticism: Critics argue that the probability of failure increases with the size, scope and complexity of the project. Technologies and practices have improved through the 1970s, 1980s, and 1990s, but the complexity in requirements and user expectations have also increased fast enough to overwhelm the improvement in practices. So, the gap between what is expected and what is delivered has not improved.

Response: This is not the fault of practitioners. This is actually a measure of the success of practitioners, because demand normally follows the supply. So customers demanding more is an obvious sign of their belief that what they demand will be supplied (even if they peg the demand slightly above the measure of supply in order to enforce agility.)

Ongoing Change

Criticism: Practitioners are eager to develop new technologies and practices and try new tools in every project. Some view this ongoing change as proof that older technologies and practices were failures.

Response: Many view this ongoing change as proof that software engineering successfully learns and grows.

Ongoing Failure

Criticism: Critics charge that incomplete or poorly designed systems are still too common. The early lessons of the field were not sufficient to prevent subsequent disasters.

Response: No field that strives to do bigger and better projects has ever avoided all unintentional failures and compromises. Moreover, traditional engineering fields frequently resort to a balance of factors to achieve optimization, and hence this is not an isolated problem.

Nothing New

Criticism: Some argue that software engineering has not created anything on its own, it merely uses what computer scientists already know.

Response: Practitioners developed many tools and practices (compilers, make, cvs, XP), on their own, out of simple need. These tools make use of the tenets of computer science, just like the other engineering fields that make use of pure sciences like math and physics.

Anyone Can Do It

Criticism: Many bright people from other fields (engineers, scientists, business people) write spreadsheet templates or calculator programs, and eventually switch to writing large applications, and believe that they do software engineering. So, software engineering is not a special skill.

Response: Software engineering is a skill that is refined through long practice. Software engineers are the ones who already have the education and experience, and they keep up with evolving technologies and practices. This is true of every skill.

We Do Not Know What It Is

Criticism: It doesn't yield to the standard ways of categorization, under accepted definitions of engineering. This is usually claimed by someone who wants to impose his/her own definition.

Response: We know a lot about what software engineering is. Software engineering is grounded in the technologies and practices, applications, and the community of software engineering practitioners.

Software as Executable Knowledge

Criticism: In Zepplins and Jet Planes [3], Philip Armour argues that software is executable knowledge, which is discovered in an creative process where trial and error, learning, and the ability to challenge one's assumptions are important. In this view, the potential benefit of software engineering is limited to making it easier for developers to trial ideas, to discover errors earlier, and to provide them with information about the state of a software system.

See also

• List of software engineering topics
• Important publications in software engineering

Referenced By