According to its homepage, the SemWeb library (great library for handling RDF under .NET) is released under GPL. Since the ROWLEX tool is built on SemWeb, ROWLEX supposed to be GPL, too. Still, ROWLEX is claimed to be released under L-GPL. Is this legally correct?
Actually, your statement is not completely accurate. SemWeb is not just GPL but dual-licensed. The source code written by Joshua Tauberer is also licensed under Creative Commons Attribution license. Since ROWLEX relies solely on the code Joshua wrote, the Creative Common Attribution license permits ROWLEX to be distributed under L-GPL.
Upon reading the Semweb licensing information, it states that it is currenly licensed under the GPL and the Creative Commons Attribution license, but that originally it was only licensed under the CC Attribution License. It also contains parts that are licensed under the LGPL, and the W3C Software License. I'm assuming that Rowlex started using the Semweb code at the point where it was only licensed under the CC, and therefore didn't have to use the the GPL.
Also, I would like to note, that there is quite a complex set of licenses here, and that somebody with more knowledge of all the different licenses might have a better explanation about what is going on.
来源：https://stackoverflow.com/questions/906808/how-can-rowlex-be-licensed-under-l-gpl-while-it-uses-semweb-which-is-gpl