Open-source license


Open-source licenses are software licenses that allow content to be used, modified, and shared. They facilitate free and open-source software development. Intellectual property laws restrict the modification and sharing of creative works. Free and open-source licenses use these existing legal structures for an inverse purpose. They grant the recipient the rights to use the software, examine the source code, modify it, and distribute the modifications. These criteria are outlined in the Open Source Definition.
After 1980, the United States began to treat software as a literary work covered by copyright law. Richard Stallman founded the free software movement in response to the rise of proprietary software. The term "open source" was used by the Open Source Initiative, founded by free-software developers Bruce Perens and Eric S. Raymond. "Open source" emphasizes the strengths of the open development model rather than software freedoms. While the goals behind the terms are different, open-source licenses and free-software licenses describe the same type of licenses.
The two main categories of open-source licenses are permissive and copyleft. Both grant permission to change and distribute software. Typically, they require attribution and disclaim liability. Permissive licenses come from academia. Copyleft licenses come from the free software movement. Copyleft licenses require derivative works to be distributed with the source code and under a similar license. Since the mid-2000s, courts in multiple countries have upheld the terms of both types of license. Software developers have filed cases as copyright infringement and as breaches of contract.

Background

is a legal category that treats creative output as property, comparable to private property. Legal systems grant the owner of an IP the right to restrict access in many ways. Owners can sell, lease, gift, or license their properties. Multiple types of IP law cover software including trademarks, patents, and copyrights.
Most countries, including the United States, have created copyright laws in line with the Berne Convention with slight variations. These laws assign a copyright whenever a work is released in any fixed format. Under US copyright law, the initial release is considered an original work. The creator, or their employer, holds the copyright to this original work and therefore has the exclusive right to make copies, release modified versions, distribute copies, perform publicly, or display the work publicly. Modified versions of the original work are derivative works. When a creator modifies an existing work, they hold the copyright to their modifications. Unless the original work was in the public domain, a derivative work can only be distributed with the permission of every copyright holder.
In 1980, the US government amended the law to treat software as a literary work. Software released after this point was restricted by IP laws. At that time, American activist and programmer Richard Stallman was working as a graduate student at the MIT Computer Science and Artificial Intelligence Laboratory. Stallman witnessed fragmentation among software developers. He blamed the spread of proprietary software and closed models of development. To push back against these trends, Stallman founded the free software movement. Throughout the 1980s, he started the GNU Project to create a free operating system, wrote essays on freedom, founded the Free Software Foundation, and wrote several free-software licenses. The FSF used existing intellectual property laws for the opposite of their intended goal of restriction. Instead of imposing restrictions, free software explicitly provided freedoms to the recipient.
File:Bruce perens 2009.jpg|alt=Photograph of Bruce Perens at a conference|thumb|Bruce Perens, author of the Open Source Definition
In the 90s, the term "open source" was coined as an alternative label for free software, and specific criteria were laid out to determine which licenses covered free and open-source software. Two active members of the free-software community, Bruce Perens and Eric S. Raymond, founded the Open Source Initiative. At Debian, Perens had proposed the Debian Free Software Guidelines. The DFSG were drafted to provide a more specific and objective standard for the FOSS that Debian would host in their repositories. The OSI adopted the DSFG and used them as the basis for their Open Source Definition. The Free Software Foundation maintains a rival set of criteria, the Free Software Definition. Historically, these three organizations and their sets of criteria have been the notable authorities in determining whether a license covers free and open-source software. There is significant diversity among individual licenses but little difference between the rival definitions. The three definitions each require that people receiving covered software must be able to use, modify, and redistribute the covered work.
Eric S. Raymond was a proponent of the term "open source" over "free software". He viewed open source as more appealing to businesses and more reflective of the tangible advantages of FOSS development. One of Raymond's goals was to expand the existing hacker community to include large commercial developers. In The Cathedral and the Bazaar, Raymond compared open-source development to the bazaar, an open-air public market. He argued that aside from ethics, the open model provided advantages that proprietary software could not replicate. Raymond focused heavily on feedback, testing, and bug reports. He contrasted the proprietary model where small pools of secretive workers carried out this work with the development of Linux where the pool of testers included potentially the entire world. He summarized this strength as "Given enough eyeballs, all bugs are shallow." The OSI succeeded in bringing open-source development to corporate developers including Sun Microsystems, IBM, Netscape, Mozilla, Apache, Apple Inc., Microsoft, and Nokia. These companies released code under existing licenses and drafted their own to be approved by the OSI.

Types

Open-source licenses are categorized as copyleft or permissive. Copyleft licenses require derivative works to include source code under a similar license. Permissive licenses do not, and therefore the code can be used within proprietary software. Copyleft can be further divided into strong and weak depending on whether they define derivative works broadly or narrowly.
Licenses focus on copyright law, but code is also covered by other forms of IP. Major open-source licenses written since the late 1990s contain patent grants. These open-source patent grants cover the patents held by the developers. Software patents cover ideas and, rather than a specific implementation, cover any implementation of a claim. Patent claims give the holder the right to exclude others from making, using, selling, or importing products based on the idea. Because patents grant the right to exclude rather than the right to create, it is possible to have a patent on an idea but still be unable to legally implement it if the invention relies on another patented idea. Thus, open-source patent grants can offer permission only from covered patents. They cannot guarantee that a third party has not patented any concepts embodied in the code. The older permissive licenses do not discuss patents directly and offer only implicit patent grants in their offers to use or sell covered material. Newer copyleft licenses and the 2004 Apache License offer explicit patent grants and limited protection from patent litigation. These patent retaliation clauses protect developers by terminating grants for any party who initiates a patent lawsuit regarding covered software.
Trademarks are the only form of IP not shared by free and open-source software. Trademarks on FOSS function the same as any other trademark. A trademark is a design that identifies the distinct source of a product. Because they distinguish products, the same designs can be used in different fields where there is no risk of confusing similar sources. To give up control of a trademark would result in the loss of that trademark. Therefore, no open-source license freely offers the use of a trademark.
Trademark restrictions can overlap copyrights and affect material otherwise freely available. The US Supreme Court described using trademark law to restrict public domain content as "mutant copyright". In Dastar Corp. v. Twentieth Century Fox Film Corp., the court "caution against misuse or over-extension of trademark" law without providing a firm decision on those mutant copyrights. Trademark overlap can leave open-source and free content projects vulnerable to a "hostile takeover" if outside parties file for trademarks on derivative works. Notably, Andrey Duskin applied for trademarks on the SCP Foundation, a collaborative writing project, when creating derivative works based on SCP stories.

Permissive

, also known as academic licenses, allow recipients to use, modify, and distribute software with no obligation to provide source code. Institutions created these licenses to distribute their creations to the public. Permissive licenses are usually short, often less than a page of text. They impose few conditions. Most include disclaimers of warranty and obligations to credit authors. A few include explicit provisions for patents, trademarks, and other forms of intellectual property.
The University of California, Berkeley created the first open-source license when they began distributing their Berkeley Software Distribution operating system. The BSD license and its later variations permit modification and distribution of the covered software. The BSD licenses brought the concept of academic freedom of ideas to computing. Early academic software authors had shared code based on implied promises. Berkeley made these concepts explicit with clear disclaimers for liability and warranty along with conditions, or clauses, for redistribution. The original had four clauses, but subsequent versions have further reduced the restrictions. As a result, it is common to specify if the covered software uses a 2-clause or 3-clause version.
The Massachusetts Institute of Technology created an academic license based on the BSD original. The MIT license clarified the conditions by making them more explicit. For example, the MIT license describes the right to sublicense. One of the strengths of open-source development is the continual process where developers can build on the derivative works of each other and combine their projects into collective works. Explicitly making covered code sublicensable provides a legal advantage when tracking the chain of authorship. The BSD and MIT are template licenses that can be adapted to any project. They are widely adapted and used by many FOSS projects.
The Apache License is more comprehensive and explicit. The Apache Software Foundation wrote it for their Apache HTTP Server. Version 2, published in 2004, offers legal advantages over simple licenses and provides similar grants. While the BSD and MIT licenses offer an implicit patent grant, the Apache License includes a section on patents with an explicit grant from contributors. Additionally, it is one of the few permissive licenses with a patent retaliation clause. Patent retaliation, or patent suspension, clauses take effect if a licensee initiates patent infringement litigation on covered code. In that situation, the patent grants are revoked. These clauses protect against patent trolling.