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

SE applications are used in wide range of activities, from industry to entertainment. Software applications improve user productivity and quality of life. Application software examples: office suites, video games, and the world wide web. System software examples: embedded systems and operating systems.

SE technologies and practices improve the productivity of developers and the quality of the applications they create. SE examples: databases, languages, libraries, patterns, and tools. CS examples: algorithms and data structures. PM examples: processes.

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.

Related terms: software engineer.

See also List of software engineering topics.

Meanings of words
As of 2004, in common parlance the term software engineering is used with at least three distinct meanings:
 * As the usual contemporary term for the broad range of activities that was formerly called programming or 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.

Levels
There are currently no clear distinctions between software engineers and non-software engineers. But, the more education and experience someone has, the clearer it is that this person is a true software engineer. The following rules of thumb have been used when hiring:


 * "Entry" SEs (who can also be called programmers) have either:
 * A CS or SE degree
 * 5 years of experience in industry


 * "Normal" SEs (who may also be called programmers) have either:
 * A CS or SE degree and 2 years of experience
 * 7 years of experience in industry


 * "Senior" SEs (who are true software engineers) have either:
 * A CS or SE degree and 5 years of experience
 * 10 years of experience in industry


 * "Very senior" SEs have some of these as well:
 * A graduate degree (ms/phd) in CS or SE
 * Published work in a CS or SE journal
 * Earned certification or license
 * Taught computing at local college or university
 * Run software projects as a manager or architect

Note: Similar levels work for other professions, such as civil engineering.

Note: Some have argued that only licensed software engineers are truly software engineers. Others have argued that only people with SE degrees are truly software engineers. But, simplistic distinctions do not work for any field.

Software engineer
Software engineering is the profession that cares about creation of software.

Members of this profession are called software engineers, programmers, developers, or practitioners.

People who write code and do not follow the doctrines of software engineering are more rightfully called programmers, developers, or software artists.

Impact of software engineering
Software engineering affects economies and societies in many ways.


 * Economic : 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.


 * Social : 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.

The debate about success
Is SE a success or a failure? Some look to the enormous economic growth and productivity gains enabled by software and claim that software engineering is a huge success. Others point to the ongoing problems with crashing applications and computer viruses and claim that software engineering has failed. How can we reconcile these points of view?

See also Debates within software engineering and Criticism of software engineering

College
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 : 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 : 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 : 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.

Undergraduate software engineering degrees are being established at many universities. A standard international curriculum for undergraduate software engineering degrees was recently defined by the CCSE.

Graduate
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.

Secondary
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.

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.

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

Processes and Methodologies
A decades-long goal has been to find processes or methodologies that improve producitivity and quality. Some want to systematize or formalize the seemingly-unruly task of writing applications. Others want to apply project management techniques to writing applications. 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.

The best-known and oldest process is the waterfall model, where (roughly) developers analyze the problem, design a solution approach, architect a software framework to that solution, develop code, test, deploy, and maintain. The problem is that adequate experience to analyze and specify large systems is almost never available and errors discovered late in the process are expensive to fix. Recent approaches (such as agile) aim to be more flexible and more incremental. These models are more complex and subtler and more realistic. Advocates urge both discipline and pragmatism.

Iterative development prescribes the construction of an 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.

'[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 practise in their university haven. But, strangely enough, the more successful university projects are carried out in a bazaar-like open-source manner.' -- Hartmut Pilch

See also software development processes and methodologies.

Roles in industry
Practitioners specialize in many roles in industry (analysts, architects, developers, testers, technical support, managers) and academia (educators, researchers).

In large projects, people may specialize in only 1 role. In small projects, people may fill several or all roles at the same time.

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

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.

See also software engineering demographics.

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 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 field in many different ways. The following paragraphs make some simple comparisons.


 * Mathematics : 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.


 * Science : Programs have many scientific properties, that are shown by measurement. For example, the performance and scalabiliy of programs under various workloads is shown by measuring them. 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.


 * Engineering : 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.


 * Manufacturing : 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 pervue of management.


 * Art : 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.


 * Performance : 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, indendent 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 empasizes 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.

History
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 struggled to write code using machine code.
 * 1950s: Early tools, such as macro assemblers and interpreters were available to improve productivity and quality.
 * 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.
 * 1970s: Colloborative software tools, such as unix, code repositories, make, and so on.
 * 1980s: Personal computers and workstations and an emphasis on process like the CMM.
 * 1990s: The WWW and 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.


 * Aspects : 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 : 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
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.


 * ICSE : 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.


 * ESEC : The European Software Engineering Conference.


 * FSE : The Foundations of Software Engineering conference is held every year, alternating between Europe and North America. It emphasizes theoretical and foundational issues.


 * CUSEC : 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 interrested in Software Engineering host the conference each year. Past guests includes Kent Beck, Joel Spolsky, Philippe Kruchten, Hal Helms, Craig Larman as well as university professors and students.

Publications

 * Important publications in software engineering

Quotes

 * [...] 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)

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