License compatibility

License compatibility is a legal framework that allows for pieces of software with different software licenses to be distributed together. The need for such a framework arises because the different licenses can contain contradictory requirements, rendering it impossible to legally combine source code from separately-licensed software in order to create and publish a new program. Proprietary licenses are generally program-specific and incompatible; authors must negotiate to combine code. Copyleft licenses are commonly deliberately incompatible with proprietary licenses, in order to prevent copyleft software from being re-licensed under a proprietary license, turning it into proprietary software. Many copyleft licenses explicitly allow relicensing under some other copyleft licenses. Permissive licenses are (with minor exceptions) compatible with everything, including proprietary licenses; there is thus no guarantee that all derived works will remain under a permissive license. License compatibility can be defined around the concepts of "collective/combined/aggregated work" and "derivative work". The first "collective work" license compatibility definition allows the usage of variously-licensed works in a combined context: the characteristic of two (or more) licenses according to which the codes distributed under these licenses may be put together in order . [emphasis added] A stronger definition includes the capability to change the license. The most prominent example is the copyleft license's demand that the "derived work" combined from code under various licenses as whole is applied to the copyleft license. License compatibility: The characteristic of a license according to which the code distributed under this license may be integrated into a bigger software that will be . [emphasis added] A combined work consists of multiple differently-licensed parts (avoiding relicensing). To achieve a combined work including copyleft licensed components (which have a viral property leading potentially to a derived work), proper isolation/separation needs to be maintained.