Software engineering

Software engineering is the profession concerned with creating and maintaining software applications by applying technologies and practices from computer science, project management, engineering, application domains, and other fields.

Software is the programs and procedures that direct computers to perform useful work. Software applications can be found in every aspect of modern life from life-critical medical-monitoring devices and nuclear power plants to entertainment video-games. Complex software guides space missions while simple software controls microwave ovens. Many software products contain millions of lines of code that are expected to perform properly in the face of changing conditions.

Software generally needs to be reliable (with the consequences of failure ranging from annoying to deadly) and needs to be produced economically. Software engineering aims to address these needs. Software engineering techniques are intended to improve the functionality and reliability of software, while improving the efficiency and easing the task of software development.

The SE community includes 630,000 practitioners and educators in the U.S. and an estimated 1,400,000 practitioners in the E.U., Asia, and elsewhere; it is about 60% the size of traditional engineering. SE pioneers include Barry Boehm, Fred Brooks, C. A. R. Hoare, and David Parnas. There is extensive debate about what SE is, who qualifies as an SE, who sets the standards, etc.

See also List of software engineering topics.




The term software engineering was used occasionally in the late 1950s and early 1960s. Software engineering was popularized by the 1968 NATO Software Engineering Conference held in Garmisch, Germany and has been in widespread use since.


As of 2005, in common parlance the term software engineering is used with a variety of distinct meanings:

  • As the usual contemporary term for the broad range of activities that was formerly called programming and systems analysis;
  • As the broad term for the technical analysis of all aspects of the practice, as opposed to the theory of computer programming;
  • As the term embodying the advocacy of a specific approach to computer programming, one that urges that it be treated as an engineering profession rather than an art or a craft, and advocates the codification of recommended practices in the form of software engineering methodologies.
  • Software engineering is "(1) the application of a systematic, disciplined, quantifiable approach to the development, operation, and maintenance of software, that is, the application of engineering to software," and "(2) the study of approaches as in (1)." -- IEEE Standard 610.12
  • Software engineers model parts of the real world in the software. As the real world changes, software must also change, and software engineering is concerned with the evolution of these models and how they meet changing requirements.

Software engineering is practiced by software engineers.

Debate over who is a software engineer

Some people believe that Software Development is a more appropriate term than Software Engineering for the process of creating software. People like Pete McBreen (author of "Software Craftsmanship") believe that the term Software Engineering implies levels of rigor and proven processes that are not appropriate for all types of software development.

Some people dispute the notion that the field is mature enough to warrant the title "engineering". In each of the last few decades, at least one radical new approach has entered the mainstream of software development (e.g. Structured Programming, Object Orientation, Agile Development), implying that the field is still changing too rapidly to be considered an engineering discipline. Other people would argue that the supposedly radical new approaches are actually evolutionary rather than revolutionary, the mere introduction of new tools rather than fundamental changes.

There are currently no widely accepted criteria for distinguishing someone who is a software engineer from someone who is not a software engineer. In addition, the industry is in the midst of a complex debate on the licensing of practicing software engineers.


For the localities that do not license software engineers, some hiring classifications are made based on education and experience. Classification levels may include: entry-level, mid-level, and senior.

Typical entry-level software engineers have a bachelor's degree and zero to five years of experience. Typical mid-level software engineers have a bachelor's or master's degree and have five to ten years of experience. Typical senior-level software engineers have an advanced degree and have ten or more years of experience. Note that these are only guidelines that are trends seen in hiring practices and that many exceptions exist.

Software engineering today

Impact of software engineering

Software engineering affects economies and societies in many ways.

In the U.S., 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 drove $1 trillion of economic and productivity growth over the last decade. Around the world, software drives economic growth in similar ways, though reliable statistics are hard to find.
Software engineering changes world culture, wherever people use computers. Email, the world-wide web, and instant messaging enable people to interact in new ways. Software lowers the cost and improves the quality of health-care, fire departments, and other important social services.

Successful projects where software engineering methods have been applied include Linux, the space shuttle software, and automatic teller machines. When it is cheaper to run a business or agency with software applications than without, businesses and agencies often invest in computers, software, and personnel.

See also software engineering economics.

Room for improvement

In spite of the enormous economic growth and productivity gains enabled by software, persistent complaints about the quality remain.

Deficient software engineering is often blamed for project failures when the blame might more properly be placed with business managers who ignore lessons already learned by Software Engineers.

See also Debates within software engineering and Criticism of software engineering


People from many different educational backgrounds make important contributions to SE. The fraction of practitioners who earn computer science or software engineering degrees has been slowly rising. Today, about 1/2 of all software engineers earn computer science or software engineering degrees. For comparison, about 3/4 of all traditional engineers earn engineering degrees.

Software degrees 
About half of all practitioners today have computer science degrees, which are the most relevant degrees that are widely available. A small, but growing, number of practitioners have software engineering degrees. As of 2004, in the U.S., about 2,000 universities offer computer science degrees and about 50 universities offer software engineering degrees. Most SE practitioners will earn computer science degrees for decades to come, though someday, this may change.
Domain degrees 
Some practitioners have degrees in application domains, bringing important domain knowledge and experience to projects. In MIS, some practitioners have business degrees. In embedded systems, some practitioners have electrical or computer engineering degrees, because embedded software often requires a detailed understanding of hardware. In medical software, some practitioners have medical informatics, general medical, or biology degrees.
Other degrees 
Some practitioners have mathematics, science, engineering, or other technical degrees. Some have philosophy, or other non-technical degrees. And, some have no degrees. Note that Barry Boehm earned degrees in mathematics and Edsger Dijkstra earned degrees in physics.


Graduate computer science degrees have been available from hundreds of universities for several decades.

Graduate software engineering degrees have been available from dozens of universities for a decade or so.


Undergraduate computer science degrees are available from most universities.

In 1996, Rochester Institute of Technology established the first BSSE degree program ( in the United States. The program received ABET accreditation in 2003. Since then, software engineering undergraduate degrees have been established at many universities. A standard international curriculum for undergraduate software engineering degrees was recently defined by the CCSE.


Programming and coding are being taught to students at an increasingly earlier stage in secondary schools. However, software engineering is not always included in the curriculum. Many have the impression that students are adequately capable of managing projects. Development techniques beyond learning a programming syntax is required .

Processes and methodologies

A decades-long goal has been to find repeatable, predictable processes or methodologies that improve productivity and quality. Some want to systematize or formalize the seemingly unruly task of writing software. Others want to apply project management techniques to writing software. Without project management, software projects can easily be delivered late or over budget. With large numbers of software projects not meeting their expectations in terms of functionality, cost, or delivery schedule, effective project management is proving difficult.

See also software development processes and methodologies.

Process steps

Software engineering requires performing many tasks, notably the following, some of which may not seem to directly produce software.

Requirements Analysis 
Extracting the requirements of a desired software product is the first task in creating it. While customers probably believe they know what the software is to do, it may require skill and experience in software engineering to recognize incomplete, ambiguous or contradictory requirements.
Specification is the task of precisely describing the software to be written, in a mathematically rigorous way. In reality, most successful specifications are written to understand and fine-tune applications that were already well-developed. Specifications are most important for external interfaces, that must remain stable.
Design and Architecture 
Design and architecture refer to determining how software is to function in a general way without being involved in details. Usually this phase is divided into two sub-phases.
Reducing a design to code may be the most obvious part of the software engineering job, but it is not necessarily the largest portion.
Testing of parts of software, especially where code by two different engineers must work together, falls to the software engineer.
An important (and often overlooked) task is documenting the internal design of software for the purpose of future maintenance and enhancement. Documentation is most important for external interfaces.
Maintaining and enhancing software to cope with newly discovered problems or new requirements can take far more time than the initial development of the software. Not only may it be necessary to add code that does not fit the original design but just determining how software works at some point after it is completed may require significant effort by a software engineer. About 2/3 of all software engineering work is maintenance, but this statistic can be misleading. A small part of that is fixing bugs. Most maintenance is extending systems to do new things, which in many ways can be considered new work. Similarly, about 2/3 of all civil engineering, architecture, and construction work is maintenance in a similar way.

Waterfall processes

The best-known and oldest process is the waterfall model, where (roughly) developers follow these steps in order. They state requirements, analyze them, design a solution approach, architect a software framework for that solution, develop code, test (perhaps unit tests then system tests), deploy, and maintain. After each step is finished, the methodology proceeds to the next step, just as builders don't revise the foundation of a house after the framing has been erected. There is no provision in the methodology for correcting errors in early steps (for example, in the requirements), so the entire (expensive) engineering process may be executed to the end, resulting in unusable or unneeded software features, just as a house built on an incorrect foundation might be uninhabitable after it is handed over to the customer. The original description of the methodology did include for iteration, but that part of the methodology is usually overlooked.

One source of difficulty is that the number of dependencies among the artifacts (outputs) of the various steps is surprisingly high, much higher in a typical software project than in a typical building project.

In old style (CMM) processes, architecture and design preceded coding, usually by separate people in a separate process step.

Although the lesson that the waterfall model doesn't work very well is known among software engineers, that lesson seems lost on many managers or executives. Perhaps the waterfall model appeals to managers because it seems to allow one to plan and carry out a software project as predictably as one might plan and build a house.

Iterative processes

Iterative development prescribes the construction of initially small but ever larger portions of a software project to help all those involved to uncover important issues early before problems or faulty assumptions can lead to disaster.

Agile processes

Agile processes are built on the foundation of iterative development. To that foundation they add a lighter, more people-centric viewpoint than traditional approaches. Agile processes use feedback, rather than planning, as their primary control mechanism. The feedback is driven by regular tests and releases of the evolving software.

Agile processes seem to be more efficient than older methodologies, using less programmer time to produce more functional, higher quality software, but have the drawback from a business perspective that they do not provide long-term planning capability. In essence, they say that they will provide the most bang for the buck, but won't say exactly what the bang will be.

Extreme Programming is the best-known agile process. In Extreme Programming, the phases are carried out in extremely small (or "continuous") steps compared to the older, "batch" processes. The (intentionally incomplete) first pass through the steps might take a day or a week, rather than the months or years of each complete step in the Waterfall Model. Writing automated tests is done first, to provide concrete goals for development. Coding (by a pair of programmers) comes next (and is complete when all the tests pass, and the programmers can't think of any more tests that should be written). Design and architecture emerge out of Refactoring, and come after coding. Design is done by the same people who do the coding. (Only the last feature - merging design and code - is common to all the other agile processes.) The incomplete but functional system is deployed or demonstrated for (some subset of) the users (at least one of which is on the development team). At this point, the practitioners start again on writing tests for the next most important part of the system.

Formal methods

Formal methods are mathematical approaches to solving software problems. Examples of formal methods are petri nets or automata theory. For instance one can build up and validate application behaviour by designing a system of finite state machines.


See also software engineering demographics.

Roles in industry

Some organizations have specialists to perform each of these tasks. Other organizations required software engineers to do many or all of them. In large projects, people may specialize in only 1 role. In small projects, people may fill several or all roles at the same time.

Specializations include: in industry (analysts, architects, developers, testers, technical support, managers) and in academia (educators, researchers).

There is considerable debate over the future employment prospects for Software Engineers and other IT Professionals. For example, an online futures market called the Future of IT Jobs in America ( attempts to answer the question as to whether there will be more IT jobs, including software engineers, in 2012 than there were in 2002.


Most software engineers work as employees or contractors. Software engineers work with businesses, government agencies (civilian or military), and non-profit organizations. Some software engineers work for themselves as free agents.


Certification is a contentious issue. Some see it as a tool to improve professional practice. Others point out that very few traditional engineers bother with any form of certification.

The most successful certification programs are oriented toward specific technologies, and are managed by the vendors of these technologies. These certification programs are tailored to the institutions that would employ people who use these technologies.

  • Microsoft ( sponsors MCSE (
  • Sun ( sponsors Java Certified Programmer (

General certification of software practitioners has struggled. The ACM had a professional certification program in the early 1980s, which was discontinued due to lack of interest. Today, the IEEE is certifying software professionals, but only about 500 people have passed the exam by March 2005.

Technologies and practices

What is the best way to make more and better software? SEs advocate many different technologies and practices, with much disagreement. This debate has gone on for 60 years and may continue forever. Software engineers use a wide variety of technologies and practices.

Practitioners use a wide variety of technologies, from compilers to word processors to code repositories.


The goal of specifications is to state what the application should do, simply and precisely. Over time, the meaning has changed.

In the 1950s, Fortran was advertised as a language that eliminated the need for programming. Engineers could literally write down the equations that they needed. Fortran was originally viewed as a specification language.

The problem is that every time languages work at a higher level, specifications are expected to work at the next level, too.

Recent approaches try to merge the specification and code into one activity, as this seems to be the only honest way to ensure the specification and code match. While Agile methods propagate specification of all requirements in code, software engineering purists argue for executable specification, which can be achieved by methods like VFSM, trying to avoid the coding activity at all.

Comparing related fields

Many fields are closely related to software engineering; here are some key similarities and distinctions. Comparing SE with other fields helps explain what SE is and helps define what SE might or should become. There is considerable debate over which fields SE most resembles (or should most resemble). These complex and inexact comparisons explain why some see software engineering as its own field.

What is the nature of SE?

Software engineering resembles many different fields in many different ways. The following paragraphs make some simple comparisons.

Programs have many mathematical properties. For example the correctness and complexity of many algorithms are mathematical concepts that can be rigorously proven. Programs are finite, so in principle, developers could know many things about a program in a mathematical way. This is often called formal methods. However, computability theory shows that not everything useful about a program can be proven. Mathematics works best for small pieces of code and has difficulty scaling up. Edsger Dijkstra has argued that software engineering is a branch of mathematics.
Programs have many scientific properties that can be measured. For example, the performance and scalability of programs under various workloads can be measured. The effectiveness of caches, bigger processors, faster networks, newer databases are scientific issues. Mathematical equations can sometimes be deduced from the measurements. Scientific approaches work best for system-wide analysis, but often are meaningless when comparing different small fragments of code.
Software Engineering is considered by many to be an engineering discipline because there are pragmatic approaches and expected characteristics of engineers. Proper analysis, documentation, and commented code are signs of an engineer. David Parnas has argued that software engineering is engineering.
Programs are built in as a sequence of steps. By properly defining and carrying out those steps, much like a manufacturing assembly line, advocates hope to improve the productivity of developers and the quality of final programs. This approach inspires the many different processes and methodologies.
Project Management 
Commercial (and many non-commercial) software projects require management. There are budgets and schedules to set. People to hire and lead. Resources (office space, computers) to acquire. All of this fits more appropriately within the purview of management.
Programs contain many artistic elements, akin to writing or painting. User interfaces should be aesthetically pleasing to users. Code should be aesthetically pleasing to programmers. Many goals of good design are NP-complete or worse (such as minimizing the number of lines of code, minimizing number of variables, etc.), meaning they are not decided objectively by either man or computer, so they must be decided by one's own sense of aesthetics. Even the decision of whether a variable name or class name is clear and simple is an artistic question. Donald Knuth famously argued that programming is an art.
The act of writing software requires that developers summon the energy to find the answers they need while they are at the keyboard. Creating software is a performance that resembles what athletes do on the field, and actors and musicians do on stage. Some argue that SEs need inspiration to spark the creation of code. Sometimes a creative spark is needed to create the architecture or develop a piece of code. Others argue that discipline is the key attribute. Pair programming emphasizes this point of view. Both Kent Beck and Watts Humphrey have argued this emphasis.

Branch of which field?

Is SE (or should SE be) a branch of programming, a branch of computer science, a branch of traditional engineering, or a field that stands on its own? There is considerable debate over this. This has important implications for professionalism, licensing, and ethics. Licensing is a polarizing issue: some fiercely advocate it while others staunchly oppose it.

Branch of programming 
Programming emphasizes writing code, independent of projects and customers. Software engineering emphasizes writing code in the context of projects and customers by making plans and delivering applications. As a branch of programming, SE would probably have no significant licensing or professionalism issues.
Branch of computer science 
Many believe that software engineering is a part of computer science, because of their close historical connections and their relationship to mathematics. They advocate keeping SE a part of computer science. Both computer science and software engineering care about programs. Computer science emphasizes the theoretical, eternal truths while software engineering emphasizes practical, everyday usefulness. Some argue that computer science is to software engineering as physics and chemistry are to traditional engineering. As a branch of computer science, SE would probably have few licensing or professionalism concerns.
Branch of engineering 
Others advocate making SE a part of traditional engineering. This is especially true for people who want to emulate other elements of engineering, such as licensing. Both engineering and software engineering share many project management problems and solutions. But, they apply different technologies, they use different kinds of processes, and are driven by different economics. As a branch of engineering, SE would probably adopt the engineering model of licensing and professionalism.
Freestanding field 
Recently, software engineering has been finding its own identity and emerging as an important freestanding field. Practitioners are slowly realizing that they form a huge community in their own right. Software engineering may need to create a form of regulation/licensing appropriate to its own circumstances.

See also Comparing software engineering and related fields.


Software engineering has a long evolving history. Both the tools that are used and the applications that are written have evolved over time. It seems likely that software engineering will continue evolving for many decades to come.

See also History of software engineering.

60 year time line

  • 1940s: First computer users wrote machine code by hand.
  • 1950s: Early tools, such as macro assemblers and interpreters were created and widely used to improve productivity and quality. First generation optimizing compilers.
  • 1960s: Second generation tools like optimizing compilers and inspections were being used to improve productivity and quality. The concept of software engineering was widely discussed. First really big (1000 programmer) projects. Commercial mainframes and custom software for big business.
  • 1970s: Collaborative software tools, such as UNIX, code repositories, make, and so on. Minicomputers and the rise of small business software.
  • 1980s: Personal computers and workstations and an emphasis on process like the CMM. The rise of consumer software.
  • 1990s: The WWW and hand-held computers make software even more widely available. Agile processes like Extreme programming.
  • 2000s: Acceptance of software engineering profession. Fight over what it means.

Future directions for software engineering

Aspect-oriented programming and agile methods are important emerging SE technologies and practices. The 2005 ICSE had tracks on both of these topics.

Aspects help programmers deal with ilities by providing tools to add or remove boilerplate code from many areas in the source code. Aspects describe how all objects or functions should behave in particular circumstances. For example, aspects can add debugging, logging, or locking control into all objects of particular types. Researchers are currently working to understand how to use aspects to design general-purpose code. Related concepts include generative programming and templates.
Agile software development guides software development projects that evolve rapidly with changing expectations and competitive markets. The heavy, document-driven processes (like TickIT, CMM and ISO 9000) are fading in importance. Some people believe that companies and agencies export many of the jobs that can be guided by heavy-weight processes. Related concepts include extreme programming and lean software development.

The Future of Software Engineering ( conference (FOSE) held at the ICSE 2000 documented the state of the art of SE in 2000 and listed many problems to be solved over the next decade. The Feyerabend project ( attempts to discover the future of software engineering by seeking and publishing innovative ideas.

Conferences, organizations and publications


Several academic conferences devoted to software engineering are held every year. There are also many other academic conferences every year devoted to special topics within SE, such as programming languages, requirements, testing, and so on.

The biggest and oldest conference devoted to software engineering is the International Conference on Software Engineering ( This conference meets every year to discuss improvements in research, education, and practice.
The European Software Engineering Conference (
The Foundations of Software Engineering ( conference is held every year, alternating between Europe and North America. It emphasizes theoretical and foundational issues.
Conferences dedicated to inform undergraduate students like the annual Canadian University Software Engineering Conference ( are also very promising for the future generation. It is completely organized by undergraduate students and lets different Canadian Universities interested in Software Engineering host the conference each year. Past guests include Kent Beck, Joel Spolsky, Philippe Kruchten, Hal Helms, Craig Larman, as well as university professors and students.



External Links


  • [...] software engineering has accepted as its charter "How to program if you cannot." (Edsger Dijkstra in The Cruelty of Really Teaching Computer Science)
  • The first step toward the management of disease was replacement of demon theories and humours theories by the germ theory. That very step, the beginning of hope, in itself dashed all hopes of magical solutions. It told workers that progress would be made stepwise, at great effort, and that a persistent, unremitting care would have to be paid to a discipline of cleanliness. So it is with software engineering today. (Fred Brooks in No Silver Bullet)
  • [SE advocates] have climbed a social ladder for a few decades and are now fighting against a tide of open source software that seems to be bringing bazaar anarchy and taking the well-deserved control out of their hands. Part of this is their utopia of "software engineering" by some magic cathedral approach which has never worked and whose failure the authors of these utopias tend to blame on the lack of control that copyright offers them over their projects. The strange thing here is that they have had the chance to put all these things into practice in their university haven. But, strangely enough, the more successful university projects are carried out in a bazaar-like open-source manner. -- Hartmut Pilchaf:Sagteware-ingenieurswese

ar:هندسة برمجيات de:Softwaretechnik es:Ingeniera de software fa:مهندسی نرم‌افزار fi:Ohjelmistotuotanto he:הנדסת תוכנה id:Rekayasa perangkat lunak it:Ingegneria informatica ja:ソフトウェア工学 lt:Programų inžinerija lv:Programminženierija nl:Software Engineering pl:Inżynieria oprogramowania pt:Engenharia de software sk:Softvérové inžinierstvo su:Rkayasa software tl:Software engineering th:วิศวกรรมซอฟต์แวร์ vi:Kỹ nghệ phần mềm zh:软件工程


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