Please correct me if I’m wrong, but I recently found myself in a pretty confusing situation and now I am unsure how to continue.
I found the jQuery.xmleditor plugin from the UNC libraries and thought it would be useful for one of our commercial products. That’s where I typically first check how a library is licensed (in this case it was Apache License 2.0, which allows redistribution under certain preconditions). I started playing around with the plugin and realized that the actual text-based editor (the part I am interested in most) was a derivative of Cloud9, which is licensed under GPLv3. That made me suspicious, because typially GPL requires GPL on derivative projects. So I started a quick web search and found out that there is indeed an incompatibility.
This licensing incompatibility applies only when some Apache project software becomes a derivative work of some GPLv3 software, because then the Apache software would have to be distributed under GPLv3. This would be incompatible with ASF’s requirement that all Apache software must be distributed under the Apache License 2.0.
For my current understanding the jQuery.xmleditor plugin is licensed wrong. However, I am not quite sure whether my current understanding is right. Can anybody perhaps enlighten me?
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The license incompatibility you found does not apply here. That restriction is a company policy of the Apache Software Foundation, but it is not part of the Apache License.
On the other hand, there is a license problem with jQuery.xmleditor. As they use code derived from a GPLv3 licensed library, the jQuery.xmleditor plugin must be distributed under the terms and conditions of the GPLv3 and everyone using the (unmodified) plugin is also bound by those terms and conditions for their project.
The fact that the GPL terms and conditions apply should have been made clear in the license information of jQuery.xmleditor.
Apart from giving incorrect information about which license terms are in effect, there are no further licensing problems. The authors of jQuery.xmleditor are within their rights to use a more permissive, GPL compatible, license for the code they wrote themselves. But those more permissive terms will only come into effect in modified versions where the GPL code has been removed.
If you are happy to comply with the GPL terms and conditions, you can go ahead and use the plugin under those terms.
Apart from that, it might be a good idea to inform the distributers of jQuery.xmleditor that the licensing information on their plugin appears to be incorrect due to their use of GPL licensed code.
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The Apache 2.0 license is compatible with the GPL v3 (but not v2): http://www.gnu.org/licenses/license-list.html#apache2
You are getting confused by the requirement that all software of the Apache Software Foundation (ASF) be licensed Apache 2.0, but that is a “company policy”. That incompatibility you are thinking about is due to the policy mandate that all ASF software is licensed per Apache 2.0, regardless of whether the licenses are compatible or not.
For other projects, where no such policy is in place, only the terms of the licenses matter, and for those situations, you can use an Apache 2.0 licensed project in your GPL v3 project, though it has to keep its Apache 2.0 license.
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