Strong, weak and non-copyleft

Posted on September 29, 2011

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Copyleft is a form of licening that is used to assure that computer software, documents and art as well as their extensions covered with it remain free (libre) for user and developers. Contraversy to copyright an authtor gives to everyone permission to copy, adapt or develope his creation, all adaptions and extensions are covered with the same licensing agreement.
Copyleft is set to guarantee everyones freedom. It isn’t contrast to copyright in meaning “no rights at all”,  author surrenders some but not all rights under copyright law.
The source code has to be available and it usually contain a copy of the license terms and acknowledge the author(s).
The  first copyleft license was  GNU General Public License,  written by Richard Stallman and its is still most used licens of copylefted software.

Strong, weak and non-copyleft

Strong copyleft provisions can be imposed to all derived works which means that the first creator of the works has the most rights. The most well known free software license that uses strong copyleft is the GNU General Public License. Strong license is also Design Science License that can apply to art, music, sports photography and video.

Weak copyleft refers to license where not all derived work inherit the copyleft license. Its inherit depends on how it was derived. Weak copyleft licenses are mostly used for software libraries by allowing links to other libraries (GNU Lesser General Public License). Most important users of weak copyright are Mozilla and OpenOffice.org.

If author wants no ownership he could just put work in public domain. Examples of non-copyleft free software licenses include the X11 license, Apache license and the BSD licenses. The X11 licence is used by the X Window System.

The Copyleft symbol can be included in HTML using following code:
<span style=”-webkit-transform:rotate(180deg);-moz-transform:rotate(180deg)
;filter:progid:DXImageTransform.Microsoft.BasicImage(rotation=2);”>
&copy;
</span>

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Posted in: IMKE, Open sourcse