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Open-source software is an antonym for closed source and refers to any computer software whose source code is available under a copyright license that permits users to study, change, and improve the software, and to redistribute it in modified or unmodified form. It is the most prominent example of open source development and often compared to user generated content .
In 1998, a group of individuals advocated  that the term free software be replaced by open-source software (OSS) as an expression which is less ambiguous and more comfortable for the corporate world. Software developers may want to publish their software with an open-source software license, so that anybody may also develop the same software or understand how it works. Open-source software generally allows anybody to make a new version of the software, port it to new operating systems and processor architectures, share it with others or market it. The aim of open source is to let the product be more understandable, modifiable, duplicatable, reliable or simply accessible, while it is still marketable.
The Open Source Definition, notably, presents an open-source philosophy, and further defines a boundary on the usage, modification and redistribution of open-source software. Software licenses grant rights to users which would otherwise be prohibited by copyright. These include rights on usage, modification and redistribution. Several open-source software licenses have qualified within the boundary of the Open Source Definition. The most prominent example is the popular GNU General Public License (GPL). While open source presents a way to broadly make the sources of a product publicly accessible, the open-source licenses allow the authors to fine tune such access.
The "open source" label came out of a strategy session held in Palo Alto in reaction to Netscape's January 1998 announcement of a source code release for Navigator (as Mozilla). A group of individuals at the session included Todd Anderson, Larry Augustin, John Hall, Sam Ockman, Christine Peterson and Eric S. Raymond. They used the opportunity before the release of Navigator's source code to clarify a potential confusion caused by the ambiguity of the word "free" in English. The 'open source' movement is generally thought to have begun with this strategy session. Many people, nevertheless, claimed that the birth of the Internet, since 1969, started the open source movement, while others do not distinguish between open source and free software movements.
The Free Software Foundation (FSF), started in 1985, intended the word 'free' to mean "free as in free speech" and not "free as in free beer." Since a great deal of free software already was (and still is) free of charge, such free software became associated with zero cost, which seemed anti-commercial.
The Open Source Initiative (OSI) was formed in February 1998 by Eric S. Raymond and Bruce Perens. With at least 20 years of evidence from case histories of closed development versus open development already provided by the Internet, the OSI presented the 'open source' case to commercial businesses, like Netscape. The OSI hoped that the usage of the label "open source," a term suggested by Peterson of the Foresight Institute at the strategy session, would eliminate ambiguity, particularly for individuals who perceive "free software" as anti-commercial. They sought to bring a higher profile to the practical benefits of freely available source code, and they wanted to bring major software businesses and other high-tech industries into open source. Perens attempted to register "open source" as a service mark for the OSI, but that attempt was impractical by trademark standards. Meanwhile, thanks to the presentation of Raymond's paper to the upper management at Netscape (Raymond only discovered when he read the Press Release, and was called by Netscape CEO Jim Barksdale's PA later in the day), Netscape released its Navigator source code as open source, with favorable results.
Critics have said that the term "open source" fosters an ambiguity of a different kind such that it confuses the mere availability of the source with the freedom to use, modify, and redistribute it. Developers have used the term Free/Open-Source Software (FOSS), or Free/Libre/Open-Source Software (FLOSS), consequently, to describe open-source software that is freely available and free of charge.
The term "Open Source" was originally intended to be trademarkable, however, the term was deemed too descriptive, so no trademark exists. The OSI would prefer that people treat Open Source as if it were a trademark, and use it only to describe software licensed under an OSI approved license. However, most writers use "open source" as a generic term rather than a trademark.
There have been instances where software vendors have labeled proprietary software as "open source" because it interfaces with popular OSS (such as Linux). Open source advocates consider this to be both confusing and incorrect.
OSI Certified is a trademark licensed only to people who are distributing software licensed under a license listed on the Open Source Initiative's list.  There is also a graphic form of the trademark, shown at right.
In his 1997 essay The Cathedral and the Bazaar, open-source evangelist Eric S. Raymond suggests a model for developing OSS known as the Bazaar model. Raymond likens the development of software by traditional methodologies to building a cathedral, "fully crafted by individual wizards or small bands of mages working in splendid isolation". He suggests that all software should be developed using the bazaar style, which he described as "a great babbling bazaar of differing agendas and approaches."
In the Cathedral, model development takes place in a centralized way. Roles are clearly defined. Roles include people dedicated to designing (the architects), people responsible for managing the project, and people responsible for implementation. Traditional software engineering follows the Cathedral model. F.P. Brooks in his book The Mythical Man-Month advocates this sort of model. He goes further to say that in order to preserve the architectural integrity of a system, the system design should be done by as few architects as possible.
The Bazaar model, however, is different. In this model, roles are not clearly defined. Gregorio Robles suggests that software developed using the Bazaar model should exhibit the following patterns:
- Users should be treated as co-developers
- The users are treated like co-developers and so they should have access to the source code of the software. Furthermore users are encouraged to submit additions to the software, code fixes for the software, bug reports, documentation etc. Having more co-developers increases the rate at which the software evolves. Linus's law states that, "Given enough eyeballs all bugs are shallow." This means that if many users view the source code they will eventually find all bugs and suggest how to fix them. Note that some users have advanced programming skills, and furthermore, each user's machine provides an additional testing environment. This new testing environment offers that ability to find and fix a new bug.
- Early Releases
- The first version of the software should be released as early as possible so as to increase one's chances of finding co-developers early.
- Frequent Integration
- New code should be integrated as often as possible so as to avoid the overhead of fixing a large number of bugs at the end of the project life cycle. Some Open Source projects have nightly builds where integration is done automatically on a daily basis.
- Several Versions
- There should be at least two versions of the software. There should be a buggier version with more features and a more stable version with fewer features. The buggy version (also called the development version) is for users who want the immediate use of the latest features, and are willing to accept the risk of using code that is not yet thoroughly tested. The users can then act as co-developers, reporting bugs and providing bug fixes. The stable version offers the users fewer bugs and fewer features.
- High Modularization
- The general structure of the software should be modular allowing for parallel development.
- Dynamic decision making structure
- There is a need for a decision making structure, whether formal or informal, that makes strategic decisions depending on changing user requirements and other factors.
Most well-known OSS products follow the Bazaar model as suggested by Eric Raymond. These include projects such as Linux, Netscape, Apache, the GNU Compiler Collection, and Perl to mention a few.
Open source licenses define the privileges and restrictions a licensor must follow in order to use, modify or redistribute the open-source software. Open-source software includes software with source code in the public domain and software distributed under an open-source license.
Examples of open source licenses include Apache License, BSD license, GNU General Public License, GNU Lesser General Public License, MIT License, Eclipse Public License and Mozilla Public License.
Open source versus closed source
The open source vs. closed source (alternatively called proprietary development) debate is sometimes heated.
Making money through traditional methods, such as sale of the use of individual copies and patent royalty payment, is more difficult and sometimes impractical with open-source software. Some closed-source advocates see open-source software as damaging to the market of commercial software. This complaint is countered by a large number of alternative funding streams such as:
- giving the software for free and instead charge for installation and support (used by many Linux distributions)
- make the software available as open-source so that people will be more likely to purchase a related product or service you do sell (e.g. OpenOffice.org vs StarOffice)
- cost avoidance / cost sharing: many developers need a product, so it makes sense to share development costs (this is the genesis of the X Window System and the Apache web server)
Studies about security in open-source software versus closed-source software show that closed-source software have fewer advisories but open-source software usually has less time between flaw discovery and a patch or fix. Advocates of closed source argue that since no one is responsible for open-source software, there is no incentive or guarantee it will be fixed, and there is nobody to take responsibility for negligence. Open-source advocates argue that since the source code of closed-source software is not available, there is no way to know what security vulnerabilities or bugs may exist. However, having the source code for a program could also make it easier for a malicious person to discover security vulnerabilities that they can take advantage of (instead of reporting or fixing them.)
Open source software versus free software
Open source software and free software are different terms for software which comes with certain rights, or freedoms, for the user. They describe two approaches and philosophies towards free software. Open source and Free software (or software libre) both describe software which is free from onerous licensing restrictions. It may be used, copied, studied, modified and redistributed without restriction. Free software is not the same as freeware, software available at zero price.
The definition of open source software was written to be almost identical to the free software definition. There are very few cases of software that is free software but is not open source software, and vice versa. The difference in the terms is where they place the emphasis. "Free software" is defined in terms of giving the user freedom. This reflects the goal of the free software movement. "Open source" highlights that the source code is viewable to all and proponents of the term usually emphasize the quality of the software and how this is caused by the development models which are possible and popular among free and open source software projects.
Free software licenses are not written exclusively by the FSF. The FSF and the OSI both list licenses which meet their respective definitions of free software. Open source software and free software share an almost identical set of licenses. One exception is an early version of the Apple Public Source License, which was accepted by the OSI but rejected by the FSF because it did not allow private modified versions; this restriction was removed in later version of the license. There are now new versions that are approved by both the OSI and the FSF.
The Open Source Initiative believes that more people will be convinced by the experience of freedom. The FSF believes that more people will be convinced by the concept of freedom. The FSF believes that knowledge of the concept is an essential requirement, insists on the use of the term free, and separates itself from the Open Source movement. The Open Source Initiative believes that free has three meanings: free as in beer, free as in freedom, and free as in unsellable. The problem with "Open Source" is it says nothing about the freedom to modify and redistribute, so it is used by people who think that source access without freedom is a sufficient definition. This possibility for misuse is the case for most of the licences that make up Microsoft's "shared source" initiative, and to a lesser extent with the "license-free" software of Daniel J. Bernstein.
In OSS development the participants, who are mostly volunteers, are distributed amongst different geographic regions so there is need for tools to aid participants to collaborate in source code development. Often these tools are also available as OSS.
Revision control systems like Concurrent Versions System (CVS) and later Subversion (svn) are examples of tools that help centrally manage the source code files and the changes to those files for a software project.
Utilities that automate testing, compiling and bug reporting help preserve stability and support of software projects that have numerous developers but no managers, quality controller or technical support. Building systems that report compilation errors among different platforms include Tinderbox. Commonly used bugtrackers include include Bugzilla and GNATS.
Tools like mailing lists and instant messaging provide means of Internet communications between developers. The Web is also a core feature of all of the above systems. Some sites centralize all the features of these tools as a software development management system, including GNU Savannah and SourceForge.
Projects and organizations
- Apache Software Foundation
- Eclipse Foundation
- Mozilla Foundation
- Open Source Development Labs
- Open Source Initiative
- Open Source Geospatial Foundation
For an extensive list of examples of open source software, see the List of open source software packages.
- Open access
- Open content for non-programming open source projects.
- Open Design the application of open source principles to creating material objects and solutions.
- Open publishing
- Openness the philosophical term
- Open source advocacy
- Open source movement
- List of open source software packages
- Open system
- Open standard
- Open format
- OpenDocument The new OASIS OpenDocument format (ODF) to create an open system for business & public sector documents.
- Free software
- Shared software
- ^ Time Magazine Dec 25 2006
- ^ a b Raymond E.S. (11 September 2000). "The Cathedral and the Bazaar". Retrieved 19 September 2004 from http://www.catb.org/~esr/writings/cathedral-bazaar/cathedral-bazaar/index.html
- ^ Robles G. (2004). "A Software Engineering approach to Libre Software". Retrieved 20 April 2005 from http://www.opensourcejahrbuch.de/2004/pdfs/III-3-Robles.pdf
- Mikko Vδlimδki, The Rise of Open Source Licensing: A Challenge to the Use of Intellectual Property in the Software Industry, Turre Publishing (2005) download PDF file (free) or order hard copy from publisher
- Free Software and Open Source software (Where to find) - from WikiHowTo
- FAQ - Getting Started With Open Source Development
- Anarchism Triumphant: Free Software and the Death of Copyright Eben Moglen, Professor of Law and History at Columbia University
- Brief History of the Open Source Movement
- "the" definition of open source
- The dotCommunist Manifesto Eben Moglen
- European Commission's Open Source Observatory The EC's IDABC Open Source Observatory is the clearinghouse of information on the use of open source software by public administrations in Europe
- Goodbye, "free software"; hello, "open source" Raymond's announcement of the term "open source", 8 February 1998
- Open Source at the Open Directory Project
- Open Source Initiative (OSI) a list of available licenses
- Open Sources: Voices from the Open Source Revolution an online book containing essays from prominent members of the open source community
- Why "Free Software" is better than "Open Source" a later essay from FSF
- Free / Open Source Research Community Many online research papers
- Jan 2006 TPOSSCON talk: "How OSS Improves Society" Aaron Siego speaks at the 2nd Trans-Pacific Open Source Software Conference in Honolulu, Hawaii.
- Why Open Source Software / Free Software (OSS/FS, FLOSS, or FOSS)? Look at the Numbers! - large collection of related quantitative studies
- UK Parliament report on Open Source (PDF)
- "Lessons from Open Source", by Jan Shafer
- Free Software Definition, Free Software Foundation Definition of free software by Richard Stallman
- Whence The Source: Untangling the Open Source/Free Software Debate, essay on the differences between Free Software and Open Source, by Thomas Scoville
- Why Free Software is better than Open Source, GNU Project essay on the differences between Free Software and Open Source, by Richard Stallman
- Degrees of Openness article explaining the different aspects of openness in computer systems, written by Adrien Lamothe, on the O'Reilly Network.
- Open Source Software List
- Differences between open source and free software as interpreted by Slackware
- Berry, D M (2004). The Contestation of Code: A Preliminary Investigation into the Discourse of the Free Software and Open Software Movement, Critical Discourse Studies, Volume 1(1).