Sunday, September 20, 2009

Open Source Licenses | Types of Licenses in Open source | What is GNU GPL , LGPL and GPL 3

Now that we are familiar with what open source is and also with its history, how do we ensure software remains open source ?

The legal instrument that regulates the use and redistribution of a computer programme is known as a software license. Proprietary software whle allowing the user to use the program, maintains that the software remains the property of the vendor and limits the uses it can be put to. Microsoft Windows, for example, forbids among other things attempts to reverse engineer it, use a copy of multiple systems and publish data related to tests among other things.

While some licenses, such as the GNU GPL makes it mandatory for the user to ensure that any derivative of the software he develops remains open source, others such as the MIT license allows the user to make the code a part of proprietary software of his own.

License under GNU GPL, are known as 'copyleft' licenses. Other methods used by the software licenses to ensure that the software remains truly open source include pratices such as patent retaliation (a Claus denying the user the open source freedoms if he attempt to patent any part of the software/ derivative developed by him). Tivoization is aimed at discouraging additional regulations through digital rights management. Most open source licenses restrict modified versions from claiming to be unmodified. some also attempt to ensure that due credit is given to the copyright holders by preventing modifications of parts of the code that print warranty or licese information.

The GNU general Public licenses, with the famous tag line "Free as in Freedom" maintain that any derivative work/modification must be keep open source and are known as copyleft licenses.

Popular examples of open source licenses include the GNU GPL. a copyleft license that demands that any modifications/ derivatives be kept copyleft. The GNULesser GPL, a more permissive version of the GNU GPL and the Apache license that requires the preservation of the copyright notice and disclaimer, but is otherwise unrestricting to further uses of the source code in both proprietary and open source programmes.

The BSD license, a completely unrestricting license that allows use of the code or derivative in any way possible.

Another example is the Mozilla Public License, a hybrid of the copyleft and non-restrictive licenses.

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