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What a License Does

A license grants outside developers certain rights that establish what they can and cannot do with the source code. The licenses we consider here grant the developer the right to use and modify the source code. Some licenses also include the right to use any intellectual property (IP), such as patents, that is embodied in the source code. Most licenses do not grant developers the right to take that IP and use it in a different application.

Each license also requires developers to assume certain responsibilities. For example, some licenses require that any bug fixes that a developer makes to the source code must be contributed back to the original author. Another common requirement is that any IP used in the source code that a developer contributes must be made available (usually without fee) to other developers who use that code.

A major area of variation among licenses is what, if anything, the developer must do in order to redistribute executable binaries built from modified versions of the source code. Many open-source licenses require that the modified source code also be made available, at no or nominal cost, to anyone who wants to see and use it--this being the whole point of open source. Some of the Sun-created licenses, SCSL and SISSL, include compatibility requirements in the license.

Some licenses allow the source code to be incorporated into a larger work that is not subject to the terms of the license, although the original source code that is being included still is; other licenses consider any additions to be extensions of the original program and subject to all of the license terms. This is a key factor to consider if you plan on combining open-source code with proprietary code.

Finally, all the licenses deal with various legal matters: warranty (typically none), liability (typically limited), termination of the license (if you violate any of its terms), dealing with brands and trademarks (typically not included with the license), and several other boilerplate issues that are also to be found in typical licenses accompanying commercial software (e.g., clauses about governing law, dispute resolution, U.S. government use, international use, and severability).