Share-Alike is a descriptive term used in the Creative Commons

Creative Commons

Creative Commons is a non-profit organization headquartered in Mountain View, California, United States devoted to expanding the range of creative works available for others to build upon legally and to share. The organization has released several copyright-licenses known as Creative Commons...

 project for copyright

Copyright

Copyright is a legal concept, enacted by most governments, giving the creator of an original work exclusive rights to it, usually for a limited time...

 licenses which include certain copyleft

Copyleft

Copyleft is a play on the word copyright to describe the practice of using copyright law to offer the right to distribute copies and modified versions of a work and requiring that the same rights be preserved in modified versions of the work...

 provisions. The Share-Alike license comes in two varieties, CC-BY-SA and CC-BY-NC-SA.

Share-alike license types

As all Creative Commons licenses, share-alike licenses require attribution

Attribution (copyright)

Attribution in copyright law, is the requirement to acknowledge or credit the author of a work which is used or appears in another work. Attribution is required by most copyright and copyleft licenses, such as the GNU Free Documentation License and Creative Commons licenses.Attribution is often...

. Share-alike means that all derivatives of a work to be licensed under the same (or a compatible) license as the original. Thus, if a person were to use parts of a BY-SA movie to create a new short film, that new short film would also need to be licensed as BY-SA. According to Creative Commons, the advantage of this license is that future users are not able to add new restrictions to a derivative of your work; their derivatives must be licensed the same way. The Share-Alike license is similar to the GNU Project

GNU Project

The GNU Project is a free software, mass collaboration project, announced on September 27, 1983, by Richard Stallman at MIT. It initiated GNU operating system development in January, 1984...

's General Public License

GNU General Public License

The GNU General Public License is the most widely used free software license, originally written by Richard Stallman for the GNU Project....

 (GPL) and Free Documentation License

GNU Free Documentation License

The GNU Free Documentation License is a copyleft license for free documentation, designed by the Free Software Foundation for the GNU Project. It is similar to the GNU General Public License, giving readers the rights to copy, redistribute, and modify a work and requires all copies and...

 (GFDL).

There are two varieties of Share-Alike licenses. The first, CC-BY-SA, allows commercial use. The second, CC-BY-NC-SA, which requires non-commercial

Non-commercial

Non-commercial refers to an activity or entity that does not in some sense involve commerce, at least relative to similar activities that do have a commercial objective or emphasis...

 use, only is Share-Alike but is not free content

Free content

Free content, or free information, is any kind of functional work, artwork, or other creative content that meets the definition of a free cultural work...

 (and not copyleft, according to some critics).

CC-BY-SA and Free Culture Works

Creative Commons Attribution-ShareAlike licenses are based on the principles of the Free Software movement

Free software movement

The free software movement is a social and political movement with the goal of ensuring software users' four basic freedoms: the freedom to run their software, to study and change their software, and to redistribute copies with or without changes. The alternative terms "software libre", "open...

. As applied to content, these principles require a license to grant the following essential freedoms to ALL users of licensed works:

• the freedom to use the work and enjoy the benefits of using it
• the freedom to study the work and to apply knowledge acquired from it
• the freedom to make and redistribute copies, in whole or in part, of the information or expression
• the freedom to make changes and improvements, and to distribute derivative works

These 4 freedoms are taken directly from the Definition of Free Culture Works
By contrast, there are also many permissive free software licences which do not require share-alike terms to be applied, thus permitting users to make modifications and improvements and apply a modified and more restrictive license.

History of ShareAlike Versions

Over the years, Creative Commons has issued 4 versions of the BY-SA and BY-NC-SA licenses (1.0, 2.0, 2.5, and 3.0).

• Attribution-ShareAlike Version 1.0 Generic - Released December, 2002http://creativecommons.org/licenses/by-sa/1.0/
  • Attribution-NonCommerical-ShareAlike Version 1.0 Generichttp://creativecommons.org/licenses/by-nc-sa/1.0/

• Attribution-ShareAlike Version 2.0 Generic - Released May, 2004http://creativecommons.org/licenses/by-sa/2.0/
  • Attribution-NonCommerical-ShareAlike Version 2.0 Generichttp://creativecommons.org/licenses/by-nc-sa/2.0/

• Attribution-ShareAlike Version 2.5 Generic - Released June, 2005http://creativecommons.org/licenses/by-sa/2.5/
  • Attribution-NonCommerical-ShareAlike Version 2.5 Generichttp://creativecommons.org/licenses/by-nc-sa/2.5/

• Attribution-ShareAlike Version 3.0 Unported - Released March, 2007http://creativecommons.org/licenses/by-sa/3.0/
  • Attribution-NonCommerical-ShareAlike Version 3.0 Unportedhttp://creativecommons.org/licenses/by-nc-sa/3.0/

  The 3.0 licenses added a compatibility clause. Creative Commons may declare a license compatible with ShareAlike, allowing it to be used instead of the exact same license for derivatives.

Adoption

In June, 2009 the Wikipedia community and Wikimedia Foundation

Wikimedia Foundation

Wikimedia Foundation, Inc. is an American non-profit charitable organization headquartered in San Francisco, California, United States, and organized under the laws of the state of Florida, where it was initially based...

 board approved the adoption of the Creative Commons Attribution-ShareAlike (CC BY-SA) license as the main content license for Wikipedia and other Wikimedia sites. This decision was hailed by many as a win for Free Culture as well as visionary leadership.

See also

• Copyleft
  Copyleft
  Copyleft is a play on the word copyright to describe the practice of using copyright law to offer the right to distribute copies and modified versions of a work and requiring that the same rights be preserved in modified versions of the work...
  
  
• Wikipedia's cc-by-sa license

External links

• Creative Commons licenses explained
• Wikipedia:Text of Creative Commons Attribution-ShareAlike 3.0 Unported License
• http://freedomdefined.org/Definition