It has been suggested that Pipeline programming be merged into this article or section. (Discuss) Proposed since August 2010.

In software engineering, a pipeline consists of a chain of processing elements (processes, threads, coroutines, etc..), arranged so that the output of each element is the input of the next. Usually some amount of buffering is provided between consecutive elements. The information that flows in these pipelines is often a stream of records, bytes or bits.

The concept is also called the pipes and filters design pattern. It was named by analogy to a physical pipeline.

Multiprocessed pipelines:- Pipelines are often implemented in a multitasking OS, by launching all elements at the same time as processes, and automatically servicing the data read requests by each process with the data written by the upstream process. In this way, the CPU will be naturally switched among the processes by the scheduler so as to minimize its idle time. In other common models, elements are implemented as lightweight threads or as coroutines to reduce the OS overhead often involved with processes. Depending upon the OS, threads may be scheduled directly by the OS or by a thread manager. Coroutines are always scheduled by a coroutine manager of some form.

Usually, read and write requests are blocking operations, which means that the execution of the source process, upon writing, is suspended until all data could be written to the destination process, and, likewise, the execution of the destination process, upon reading, is suspended until at least some of the requested data could be obtained from the source process. Obviously, this cannot lead to a deadlock, where both processes would wait indefinitely for each other to respond, since at least one of the two processes will soon thereafter have its request serviced by the operating system, and continue to run.

For performance, most operating systems implementing pipes use pipe buffers, which allow the source process to provide more data than the destination process is currently able or willing to receive. Under most Unices and Unix-like operating systems, a special command is also available which implements a pipe buffer of potentially much larger and configurable size, typically called "buffer". This command can be useful if the destination process is significantly slower than the source process, but it is anyway desired that the source process can complete its task as soon as possible. E.g., if the source process consists of a command which reads an audio track from a CD and the destination process consists of a command which compresses the waveform audio data to a format like MP3. In this case, buffering the entire track in a pipe buffer would allow the CD drive to spin down more quickly, and enable the user to remove the CD from the drive before the encoding process has finished.

Such a buffer command can be implemented using available operating system primitives^{[disambiguation needed ]} for reading and writing data. Wasteful busy waiting can be avoided by using facilities such as poll or select or multithreading.

VM/CMS and MVS[link]

CMS Pipelines is a port of the pipeline idea to VM/CMS and MVS systems. It supports much more complex pipeline structures than Unix shells, with steps taking multiple input streams and producing multiple output streams. (Such functionality is supported by the Unix kernel, but few programs use it as it makes for complicated syntax and blocking modes, although some shells do support it via arbitrary file descriptor assignment). Due to the different nature of IBM mainframe operating systems, it implements many steps inside CMS Pipelines which in Unix are separate external programs, but can also call separate external programs for their functionality. Also, due to the record-oriented nature of files on IBM mainframes, pipelines operate in a record-oriented, rather than stream-oriented manner.^{[citation needed]}

Pseudo-pipelines[link]

On single-tasking operating systems, the processes of a pipeline have to be executed one by one in sequential order; thus the output of each process must be saved to a temporary file, which is then read by the next process. Since there is no parallelism or CPU switching, this version is called a "pseudo-pipeline".

For example, the command line interpreter of MS-DOS ('COMMAND.COM') provides pseudo-pipelines with a syntax superficially similar to that of Unix pipelines. The command "dir | sort | more" would have been executed like this (albeit with more complicated temporary file names):

1. Create temporary file 1.tmp
2. Run command "dir", redirecting its output to 1.tmp
3. Create temporary file 2.tmp
4. Run command "sort", redirecting its input to 1.tmp and its output to 2.tmp
5. Run command "more", redirecting its input to 2.tmp, and presenting its output to the user
6. Delete 1.tmp and 2.tmp, which are no longer needed
7. Return to the command prompt

All temporary files are stored in the directory pointed to by %TEMP%, or the current directory if %TEMP% isn't set.

Thus, pseudo-pipes acted like true pipes with a pipe buffer of unlimited size (disk space limitations notwithstanding), with the significant restriction that a receiving process could not read any data from the pipe buffer until the sending process finished completely. Besides causing disk traffic, if one doesn't install a harddisk cache such as SMARTDRV, that would have been unnecessary under multi-tasking operating systems, this implementation also made pipes unsuitable for applications requiring real-time response, like, for example, interactive purposes (where the user enters commands that the first process in the pipeline receives via stdin, and the last process in the pipeline presents its output to the user via stdout).

Also, commands that produce a potentially infinite amount of output, such as the yes command, cannot be used in a pseudo-pipeline, since they would run until the temporary disk space is exhausted, so the following processes in the pipeline could not even start to run.

Object pipelines[link]

Beside byte stream-based pipelines, there are also object pipelines. In an object pipeline, the processes output objects instead of texts; therefore removing the string parsing tasks that are common in UNIX shell scripts. Windows PowerShell uses this scheme and transfers .NET objects. Channels, found in the Limbo programming language, and the IPython ipipe extension are other examples of this metaphor.

Pipelines in GUIs[link]

Graphical environments such as RISC OS and ROX Desktop also make use of pipelines. Rather than providing a save dialog box containing a file manager to let the user specify where a program should write data, RISC OS and ROX provide a save dialog box containing an icon (and a field to specify the name). The destination is specified by dragging and dropping the icon. The user can drop the icon anywhere an already-saved file could be dropped, including onto icons of other programs. If the icon is dropped onto a program's icon, it's loaded and the contents that would otherwise have been saved are passed in on the new program's standard input stream.

For instance, a user browsing the world-wide web might come across a .gz compressed image which they want to edit and re-upload. Using GUI pipelines, they could drag the link to their de-archiving program, drag the icon representing the extracted contents to their image editor, edit it, open the save as dialog, and drag its icon to their uploading software.

Conceptually, this method could be used with a conventional save dialog box, but this would require the user's programs to have an obvious and easily accessible location in the filesystem that can be navigated to. In practice, this is often not the case, so GUI pipelines are rare.

Other considerations[link]

The name 'pipeline' comes from a rough analogy with physical plumbing in that a pipeline usually^[1] allows information to flow in only one direction, like water often flows in a pipe.

Pipes and filters can be viewed as a form of functional programming, using byte streams as data objects; more specifically, they can be seen as a particular form of monad for I/O^[2].

The concept of pipeline is also central to the Cocoon web development framework or to any XProc (the W3C Standards) implementations, where it allows a source stream to be modified before eventual display.

This pattern encourages the use of text streams as the input and output of programs. This reliance on text has to be accounted when creating graphic shells to text programs.

History[link]

Process pipelines were invented by Douglas McIlroy, one of the designers of the first Unix shells, and greatly contributed to the popularity of that operating system. It can be considered the first non-trivial instance of software componentry.

The idea was eventually ported to other operating systems, such as DOS, OS/2, Windows NT, BeOS, AmigaOS, MorphOS and Mac OS X (the latter being a UNIX OS).

See also[link]

• Anonymous pipe
• Component-based software engineering
• GStreamer for a multimedia framework built on plugin pipelines
• Named pipe, an operating system construct intermediate to anonymous pipe and file.
• Pipeline (computing) for other computer-related versions of the concept.
• Pipeline (Unix) for details specific to Unix.
• Plumber - "intelligent pipes" developed as part of Plan 9
• Programming in the large
• Software design pattern
• producer-consumer problem for implementation aspects of software pipelines.
• XML pipeline for processing of XML files

Notes[link]

1. ^ There are exceptions, such as "broken pipe" signals.
2. ^ "Monadic I/O and UNIX shell programming"

External links[link]

• Pipeline Processing.
• Parallel Programming: Do you know Pipeline Parallelism?

• Pipeline transport, a conduit made from pipes connected end-to-end for long-distance fluid transport
• Plastic Pressure Pipe Systems, for fluid handling
• Milking pipeline, used on a dairy farm to transport fluid milk
• Pipeline (computing), a chain of data-processing stages or a CPU optimization found on
  • Classic RISC pipeline, a five stage hardware based computer instruction set.
  • Pipeline (software), a chain of data-processing processes or other software entities
  • Graphics pipeline, the method of rasterization-based rendering as supported by graphics hardware
  • Pipeline (Unix), a set of process chained by their standard streams
  • XML pipeline, a connection of XML transformations
• Telestream pipeline, a video capture and playout hardware device
• Sales pipeline, a visualisation of the sales process of a company
• The Pipeline, a former internet service provider

Places[link]

• Banzai Pipeline, a surfing spot on the North Shore of Oahu
  • Mister Pipeline, an Oahu surfer title
• Tolt pipeline trail, an equestrian and biking trail in Redmond, Washington, USA and Canada

Entertainment[link]

• "Pipeline" (song), a 1963 song by surf rock band The Chantays, also recorded by Johnny Thunders, Hank Marvin, The Ventures and Dick Dale, the Del-Tones, Agent Orange, and Anthrax
• Pipeline (game), a 1989 computer game for the BBC Micro and Acorn Electron
• Pipeline Instrumental Review, a music magazine dedicated to instrumental music
• CNN Pipeline, a streaming video service by CNN
• "Pipeline" (instrumental), a song by The Alan Parsons Project from the album Ammonia Avenue
• Pipeline Music, a record label
• Pipeline (comics), a character from Marvel Comics with the ability to teleport himself and others
• Pipeline (board game), winner of Games Magazine's 1992 Game of the Year award
• Radio Scotland programme of music on the bagpipes

This disambiguation page lists articles associated with the same title. If an internal link led you here, you may wish to change the link to point directly to the intended article.

Computer software, or just software, is a collection of computer programs and related data that provides the instructions for telling a computer what to do and how to do it. Software refers to one or more computer programs and data held in the storage of the computer for some purposes. In other words, software is a set of programs, procedures, algorithms and its documentation concerned with the operation of a data processing system. Program software performs the function of the program it implements, either by directly providing instructions to the computer hardware or by serving as input to another piece of software. The term was coined to contrast to the old term hardware (meaning physical devices). In contrast to hardware, software "cannot be touched".^[1] Software is also sometimes used in a more narrow sense, meaning application software only. Sometimes the term includes data that has not traditionally been associated with computers, such as film, tapes, and records.^[2]

Computer software is so called to distinguish it from computer hardware, which encompasses the physical interconnections and devices required to store and execute (or run) the software. At the lowest level, executable code consists of machine language instructions specific to an individual processor. A machine language consists of groups of binary values signifying processor instructions that change the state of the computer from its preceding state. Programs are an ordered sequence of instructions for changing the state of the computer in a particular sequence. It is usually written in high-level programming languages that are easier and more efficient for humans to use (closer to natural language) than machine language. High-level languages are compiled or interpreted into machine language object code. Software may also be written in an assembly language, essentially, a mnemonic representation of a machine language using a natural language alphabet. Assembly language must be assembled into object code via an assembler.

History[link]

This section may need to be rewritten entirely to comply with Wikipedia's quality standards. You can help. The discussion page may contain suggestions. (January 2012)

The first theory about software was proposed by Alan Turing in his 1935 essay Computable numbers with an application to the Entscheidungsproblem (Decision problem).^[3] The term "software" was first used in print by John W. Tukey in 1958.^[4] Colloquially, the term is often used to mean application software. In computer science and software engineering, software is all information processed by computer system, programs and data.^[4] The academic fields studying software are computer science and software engineering.

The history of computer software is most often traced back to the first software bug in 1946^{[citation needed]}. As more and more programs enter the realm of firmware, and the hardware itself becomes smaller, cheaper and faster as predicted by Moore's law, elements of computing first considered to be software, join the ranks of hardware. Most hardware companies today have more software programmers on the payroll than hardware designers^{[citation needed]}, since software tools have automated many tasks of Printed circuit board engineers. Just like the Auto industry, the Software industry has grown from a few visionaries operating out of their garage with prototypes. Steve Jobs and Bill Gates were the Henry Ford and Louis Chevrolet of their times^{[citation needed]}, who capitalized on ideas already commonly known before they started in the business. In the case of Software development, this moment is generally agreed to be the publication in the 1980s of the specifications for the IBM Personal Computer published by IBM employee Philip Don Estridge. Today his move would be seen as a type of crowd-sourcing.

Until that time, software was bundled with the hardware by Original equipment manufacturers (OEMs) such as Data General, Digital Equipment and IBM^{[citation needed]}. When a customer bought a minicomputer, at that time the smallest computer on the market, the computer did not come with Pre-installed software, but needed to be installed by engineers employed by the OEM. Computer hardware companies not only bundled their software, they also placed demands on the location of the hardware in a refrigerated space called a computer room. Most companies had their software on the books for 0 dollars, unable to claim it as an asset (this is similar to financing of popular music in those days). When Data General introduced the Data General Nova, a company called Digidyne wanted to use its RDOS operating system on its own hardware clone. Data General refused to license their software (which was hard to do, since it was on the books as a free asset), and claimed their "bundling rights". The Supreme Court set a precedent called Digidyne v. Data General in 1985. The Supreme Court let a 9th circuit decision stand, and Data General was eventually forced into licensing the Operating System software because it was ruled that restricting the license to only DG hardware was an illegal tying arrangement.^[5] Soon after, IBM 'published' its DOS source for free,^{[citation needed]} and Microsoft was born. Unable to sustain the loss from lawyer's fees, Data General ended up being taken over by EMC Corporation. The Supreme Court decision made it possible to value software, and also purchase Software patents. The move by IBM was almost a protest at the time. Few in the industry believed that anyone would profit from it other than IBM (through free publicity). Microsoft and Apple were able to thus cash in on 'soft' products. It is hard to imagine today that people once felt that software was worthless without a machine. There are many successful companies today that sell only software products, though there are still many common software licensing problems due to the complexity of designs and poor documentation, leading to patent trolls.

With open software specifications and the possibility of software licensing, new opportunities arose for software tools that then became the de facto standard, such as DOS for operating systems, but also various proprietary word processing and spreadsheet programs. In a similar growth pattern, proprietary development methods became standard Software development methodology.

Types of software[link]

A layer structure showing where the operating system software and application software are situated while running on a typical desktop computer

Software includes all the various forms and roles that digitally stored data may have and play in a computer (or similar system), regardless of whether the data is used as code for a CPU, or other interpreter, or whether it represents other kinds of information. Software thus encompasses a wide array of products that may be developed using different techniques such as ordinary programming languages, scripting languages, microcode, or an FPGA configuration.

The types of software include web pages developed in languages and frameworks like HTML, PHP, Perl, JSP, ASP.NET, XML, and desktop applications like OpenOffice.org, Microsoft Word developed in languages like C, C++, Objective-C, Java, C#, or Smalltalk. Application software usually runs on an underlying software operating systems such as Linux or Microsoft Windows. Software (or firmware) is also used in video games and for the configurable parts of the logic systems of automobiles, televisions, and other consumer electronics.

Practical computer systems divide software systems into three major classes^{[citation needed]}: system software, programming software and application software, although the distinction is arbitrary, and often blurred.

System software[link]

System software is computer software designed to operate the computer hardware to provide basic functionality and to provide a platform for running application software.^[6][7] System software includes device drivers, operating systems, servers, utilities, and window systems.

System software is responsible for managing a variety of independent hardware components, so that they can work together harmoniously. Its purpose is to unburden the application software programmer from the often complex details of the particular computer being used, including such accessories as communications devices, printers, device readers, displays and keyboards, and also to partition the computer's resources such as memory and processor time in a safe and stable manner.

Programming software[link]

Programming software include tools in the form of programs or applications that software developers use to create, debug, maintain, or otherwise support other programs and applications. The term usually refers to relatively simple programs such as compilers, debuggers, interpreters, linkers, and text editors, that can be combined together to accomplish a task, much as one might use multiple hand tools to fix a physical object. Programming tools are intended to assist a programmer in writing computer programs, and they may be combined in an integrated development environment (IDE) to more easily manage all of these functions.

Application software[link]

Application software is developed to perform in any task that benefits from computation. It is a set of programs that allows the computer to perform a specific data processing job for the user. It is a broad category, and encompasses software of many kinds, including the internet browser being used to display this page. This category includes:

• Business software
• Computer-aided design
• Databases
• Decision-making software
• Educational software
• Image editing
• Industrial automation
• Mathematical software
• Medical software
• Molecular modeling software
• Quantum chemistry and solid state physics software
• Simulation software
• Spreadsheets
• Telecommunications (i.e., the Internet and everything that flows on it)
• Video editing software
• Video games
• Word processing

Software topics[link]

Architecture[link]

Users often see things differently than programmers. People who use modern general purpose computers (as opposed to embedded systems, analog computers and supercomputers) usually see three layers of software performing a variety of tasks: platform, application, and user software.

• Platform software: Platform includes the firmware, device drivers, an operating system, and typically a graphical user interface which, in total, allow a user to interact with the computer and its peripherals (associated equipment). Platform software often comes bundled with the computer. On a PC you will usually have the ability to change the platform software.
• Application software: Application software or Applications are what most people think of when they think of software. Typical examples include office suites and video games. Application software is often purchased separately from computer hardware. Sometimes applications are bundled with the computer, but that does not change the fact that they run as independent applications. Applications are usually independent programs from the operating system, though they are often tailored for specific platforms. Most users think of compilers, databases, and other "system software" as applications.
• User-written software: End-user development tailors systems to meet users' specific needs. User software include spreadsheet templates and word processor templates. Even email filters are a kind of user software. Users create this software themselves and often overlook how important it is. Depending on how competently the user-written software has been integrated into default application packages, many users may not be aware of the distinction between the original packages, and what has been added by co-workers.

Documentation[link]

Most software has software documentation so that the end user can understand the program, what it does, and how to use it. Without clear documentation, software can be hard to use—especially if it is very specialized and relatively complex like Photoshop or AutoCAD.

Developer documentation may also exist, either with the code as comments and/or as separate files, detailing how the programs works and can be modified.

Library[link]

An executable is almost always not sufficiently complete for direct execution. Software libraries include collections of functions and functionality that may be embedded in other applications. Operating systems include many standard Software libraries, and applications are often distributed with their own libraries.

Standard[link]

Since software can be designed using many different programming languages and in many different operating systems and operating environments, software standard is needed so that different software can understand and exchange information between each other. For instance, an email sent from a Microsoft Outlook should be readable from Yahoo! Mail and vice versa.

Execution[link]

Computer software has to be "loaded" into the computer's storage (such as the hard drive or memory). Once the software has loaded, the computer is able to execute the software. This involves passing instructions from the application software, through the system software, to the hardware which ultimately receives the instruction as machine code. Each instruction causes the computer to carry out an operation – moving data, carrying out a computation, or altering the control flow of instructions.

Data movement is typically from one place in memory to another. Sometimes it involves moving data between memory and registers which enable high-speed data access in the CPU. Moving data, especially large amounts of it, can be costly. So, this is sometimes avoided by using "pointers" to data instead. Computations include simple operations such as incrementing the value of a variable data element. More complex computations may involve many operations and data elements together.

Quality and reliability[link]

Software quality is very important, especially for commercial and system software like Microsoft Office, Microsoft Windows and Linux. If software is faulty (buggy), it can delete a person's work, crash the computer and do other unexpected things. Faults and errors are called "bugs." Many bugs are discovered and eliminated (debugged) through software testing. However, software testing rarely – if ever – eliminates every bug; some programmers say that "every program has at least one more bug" (Lubarsky's Law). All major software companies, such as Microsoft, Novell and Sun Microsystems, have their own software testing departments with the specific goal of just testing. Software can be tested through unit testing, regression testing and other methods, which are done manually, or most commonly, automatically, since the amount of code to be tested can be quite large. For instance, NASA has extremely rigorous software testing procedures for many operating systems and communication functions. Many NASA based operations interact and identify each other through command programs called software. This enables many people who work at NASA to check and evaluate functional systems overall. Programs containing command software enable hardware engineering and system operations to function much easier together.

License[link]

The software's license gives the user the right to use the software in the licensed environment. Some software comes with the license when purchased off the shelf, or an OEM license when bundled with hardware. Other software comes with a free software license, granting the recipient the rights to modify and redistribute the software. Software can also be in the form of freeware or shareware.

Patents[link]

Software can be patented in some but not all countries; however, software patents can be controversial in the software industry with many people holding different views about it. The controversy over software patents is about specific algorithms or techniques that the software contains, which may not be duplicated by others and considered intellectual property and copyright infringement depending on the severity.

Design and implementation[link]

Design and implementation of software varies depending on the complexity of the software. For instance, design and creation of Microsoft Word software will take much more time than designing and developing Microsoft Notepad because of the difference in functionalities in each one.

Software is usually designed and created (coded/written/programmed) in integrated development environments (IDE) like Eclipse, Emacs and Microsoft Visual Studio that can simplify the process and compile the program. As noted in different section, software is usually created on top of existing software and the application programming interface (API) that the underlying software provides like GTK+, JavaBeans or Swing. Libraries (APIs) are categorized for different purposes. For instance, JavaBeans library is used for designing enterprise applications, Windows Forms library is used for designing graphical user interface (GUI) applications like Microsoft Word, and Windows Communication Foundation is used for designing web services. Underlying computer programming concepts like quicksort, hashtable, array, and binary tree can be useful to creating software. When a program is designed, it relies on the API. For instance, if a user is designing a Microsoft Windows desktop application, he/she might use the .NET Windows Forms library to design the desktop application and call its APIs like Form1.Close() and Form1.Show()^[8] to close or open the application and write the additional operations him/herself that it need to have. Without these APIs, the programmer needs to write these APIs him/herself. Companies like Sun Microsystems, Novell, and Microsoft provide their own APIs so that many applications are written using their software libraries that usually have numerous APIs in them.

Computer software has special economic characteristics that make its design, creation, and distribution different from most other economic goods.^{[specify][9][10]}

A person who creates software is called a programmer, software engineer, software developer, or code monkey, terms that all have a similar meaning.

Industry and organizations[link]

A great variety of software companies and programmers in the world comprise a software industry. Software can be quite a profitable industry: Bill Gates, the founder of Microsoft was the richest person in the world in 2009 largely by selling the Microsoft Windows and Microsoft Office software products. The same goes for Larry Ellison, largely through his Oracle database software. Through time the software industry has become increasingly specialized.

Non-profit software organizations include the Free Software Foundation, GNU Project and Mozilla Foundation. Software standard organizations like the W3C, IETF develop software standards so that most software can interoperate through standards such as XML, HTML, HTTP or FTP.

Other well-known large software companies include Novell, SAP, Symantec, Adobe Systems, and Corel, while small companies often provide innovation.

See also[link]

	Software portal
	Free software portal

• List of software
• Personal computer hardware

References[link]

External links[link]

Wikimedia Commons has media related to: Software

Look up software in Wiktionary, the free dictionary.

• Software Wikia

This article needs additional citations for verification. Please help improve this article by adding citations to reliable sources. Unsourced material may be challenged and removed. (August 2010)

A software developer is a person concerned with facets of the software development process. Their work includes researching, designing, developing, and testing software.^[1] A software developer may take part in design, computer programming, or software project management. They may contribute to the overview of the project on the application level rather than component-level or individual programming tasks. Software developers are often still guided by lead programmers but the description also encompasses freelance software developers.

In the US, a software developer is classified into one of 3 titles (all under the 15-0000 Computer and Mathematical Occupations Major Group):^[2]

1. 15-1131 Computer Programmers^[3]
2. 15-1132 Software Developers, Applications^[4]
3. 15-1133 Software Developers, Systems Software^[5]

A person who develops stand-alone software (that is more than just a simple program) and got involved with all phases of the development (design and code) is a software developer.^{[citation needed]} Some of the notable software people include Peter Norton (developer of Norton Utilities), Richard Garriott (Ultima-series creator), and Philippe Kahn (Borland key founder), all of whom started as entrepreneurial individual or small-team software developers before becoming rich and famous.

Other names which are often used in the same close context are programmer, software analyst, and software engineer.

According to developer Eric Sink, the differences between system design, software development and programming are more apparent. Already in the current market place there can be found a segregation between programmers and developers,^{[dubious – discuss]} being that one who implements is not the same as the one who designs the class structure or hierarchy. Even more so that developers become systems architects, those who design the multi-leveled architecture or component interactions of a large software system.^[6] (see also Debate over who is a software engineer)

Aspects of developer's job may include:

• Software design
• Actual core implementation (programming which is often the most important portion of software development)
• Other required implementations (e.g. installation, configuration, customization, integration, data migration)
• Participation in software product definition, including business case or gap analysis
• Specification
• Requirements analysis
• Development and refinement of throw-away simulations or prototypes to confirm requirements
• Feasibility and cost–benefit analysis, including the choice of application architecture and framework, leading to the budget and schedule for the project
• Authoring of documentation needed by users and implementation partners etc.
• Testing, including defining/supporting acceptance testing and gathering feedback from pre-release testers
• Participation in software release and post-release activities, including support for product launch evangelism (e.g. developing demonstrations and/or samples) and competitive analysis for subsequent product build/release cycles
• Maintenance

In a large company, there may be employees whose sole responsibility may consist of only one of the phases above. In smaller development environments, a few, or even a single individual might handle the complete process.

Separation of concerns[link]

In more mature engineering disciplines such as mechanical, civil and electrical engineering, the designers are separate from the implementers. That is, the engineers who generate design documents are not the same individuals who actually build things (such as mechanical parts, circuits, or roads, for instance). In software engineering, it is more common to have the architecture, design, implementation, and test functions performed by a single individual. In particular, the design and implementation of source code is commonly integrated.^{[citation needed]}

This resembles the early phases of industrialization in which individuals would both design and build things. More mature organizations have separate test groups, but the architecture, design, implementation, and unit test functions are often performed by the same highly trained individuals.^{[citation needed]}

References[link]