| The licenses described in this chapter are very different from those described in Chapter 2. These licenses impose substantial limitations on those who create and distribute derivative works based on works that use these licenses. The GNU General Public License (the GPL License) explicitly requires that derivative works be distributed under the terms of the GPL License and also that derivative works may only be permitted to be distributed under the terms of the license. The Mozilla License imposes different and less restrictive terms on the licensing of derivative works. Both of these licenses (and a variation of the GPL License) are described in some detail in the following sections. Before going into detailed descriptions of these licenses and their effects, it's a good idea to re-examine the limitations imposed by the licenses described in the previous chapter, if only for contrast. The MIT License, probably the simplest of those licenses, imposes almost no restrictions on licensees and no meaningful restriction at all on licensees distributing derivative works. When the original work or "substantial portions" of it are distributed, the licensee is required to include a copyright notice and the notice giving permission to potential licensees of their rights to use the work. The licensee is not even required to include the disclaimer of warranties that was part of the original license. (Such licensees may, however, have good reason to include that disclaimer in particular, to protect themselves from potential liability.) The MIT License does not impose even these restrictions on licensees who choose not to distribute it or "substantial portions" of it, but rather only works derived from it. Such licensees need not include the copyright notice, the disclaimer of warranties, or the permission notice. As described in the previous chapter, this allows the creator of a derivative work to license that new work in any way that he may choose, whether under a proprietary license or under the MIT or another open source license. By contrast, the BSD License, both pre- and post-1999, imposes explicit limitations on distribution of both the original and derivative works.[1] These limitations include the inclusion of the enumerated terms of the license so that these limitations will also govern the use of the derivative work: the non-endorsement provision, the copyright notice, the acknowledgment of the creator of the original work, and the inclusion of the disclaimer of warranties. These enumerated limitations, however, do not require that the creator of the derivative work license under terms no more restrictive than those applicable to the original work. Accordingly, as noted in the previous chapter, so long as these conditions are complied with, the creator of the derivative work may then license that work under a proprietary license, under another open source license, or under the BSD License, so long as the terms of that license do not conflict with the limitations of the BSD License. There is no requirement, for example, that the creator of the derivative work make the source code of that work available to others. [1] The BSD license phrases this as "Redistribution and use [of the work] in source and binary forms, with or without modification," a clause that seems intended to govern the distribution of both the original and derivative works. Whether a derivative work that incorporated only a small part of the BSD licensed work could reasonably be described as a "work . . . with modification" is, admittedly, arguable. A better reading of the license would bring derivative works within the enumerated restrictions, as this appears to be the intent of the license's drafters.
The licenses discussed in this chapter impose much more specific limitations on the way in which derivative works may be licensed. Essentially, by using a work licensed under the GPL, the LGPL, or the Mozilla Licenses, the licensee is agreeing not only to respect those limitations with regard to his or her own use of the licensed work but to impose those limitations (and with regard to the GPL and LGPL Licenses only those limitations) on licensees of any derivative work that he or she may choose to create from the original work. |
