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I have used many open source software but I seldom looked at their licenses in detail. I took it for granted for a long

time that open source software is software you can acquire for free including the source code and you can do whatever you want with it commercially or non-commercially. If open source software is that simple and straight forward then why would it need a license at all? I was wondering about that for a long time and I decided to take a serious look. I found software licensing issue is overwhelmingly complicate and here is what I learn so far.

Generally if software meets the principles set forth by Open Source Initiative (OSI) then it is open source software. You can find those principles on www.opensource.org and they are reiterated as the following

1. Free Redistribution
   The license shall not restrict any party from selling or giving away the software as a component of an aggregate software distribution containing programs from several different sources. The license shall not require a royalty or other fee for such sale.
2. Source Code
   The program must include source code, and must allow distribution in source code as well as compiled form. Where some form of a product is not distributed with source code, there must be a well-publicized means of obtaining the source code for no more than a reasonable reproduction cost preferably, downloading via the Internet without charge. The source code must be the preferred form in which a programmer would modify the program. Deliberately obfuscated source code is not allowed. Intermediate forms such as the output of a preprocessor or translator are not allowed.
3. Derived Works
   The license must allow modifications and derived works, and must allow them to be distributed under the same terms as the license of the original software.
4. Integrity of The Author’s Source Code
   The license may restrict source-code from being distributed in modified form only if the license allows the distribution of “patch files” with the source code for the purpose of modifying the program at build time. The license must explicitly permit distribution of software built from modified source code. The license may require derived works to carry a different name or version number from the original software.
5. No Discrimination Against Persons or Groups
   The license must not discriminate against any person or group of persons.
6. No Discrimination Against Fields of Endeavor
   The license must not restrict anyone from making use of the program in a specific field of endeavor. For example, it may not restrict the program from being used in a business, or from being used for genetic research.
7. Distribution of License
   The rights attached to the program must apply to all to whom the program is redistributed without the need for execution of an additional license by those parties.
8. License Must Not Be Specific to a Product
   The rights attached to the program must not depend on the program’s being part of a particular software distribution. If the program is extracted from that distribution and used or distributed within the terms of the program’s license, all parties to whom the program is redistributed should have the same rights as those that are granted in conjunction with the original software distribution.
9. License Must Not Restrict Other Software
   The license must not place restrictions on other software that is distributed along with the licensed software. For example, the license must not insist that all other programs distributed on the same medium must be open-source software.
10. License Must Be Technology-Neutral
    No provision of the license may be predicated on any individual technology or style of interface.

However open source license models can be based on these principles and have added restrictions. Two of the most widely use open source licensing model is GPL and BSD.

GPL

GPL is also known as GNU general public license. It was created by Richard Stallman in 1989. The basic idea of this license model is to ensure the freedom of software forever. It states that you are allowed to use the software on the condition that any derivative works that you create from it must carry the same license.

In other words if you acquire GPL software you are free to do whatever you want with it like adding your own enhancement and repackaging it and selling it. But your enhancement has to carry the same GPL license. That means the people who receives your enhancement can do whatever they want with them also. In essence it is a license that guarantees that free software cannot become non-free. It doesn’t mean that you can’t sell your enhancement for money though. At lease you can make some money of your first customer right?

For more detail on GPL license stipulations you refer to this site.

BSD

BSD is known as Berkeley Software Distribution. It was created by the University of California. It is a licensing model with more freedom then GPL. GPL prevents you taking the open source code modifying it and then making it proprietary. But with BSD model you can do that so long as you retain the copy right notice in your source code. That is a very minimum restriction.

For more information on BSD you can check out this out.

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