Extension License

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Extension License

Juan Carlos Prieto
Dear all, 

I would like to confirm if an extension using software licensed GPL falls into the "Category 2" extension and is compatible with Slicer's BSD license. 

Would the only requirement be that the software package does not compile/link against Slicer's core? 

Thank you in advance, 

--
Juan Carlos Prieto
Research Assistant Professor
University of North Carolina, Chapel Hill. 
phone: 919 843 9497

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Re: Extension License

Steve Pieper-2
Hi Juan - 

Thanks for bringing this up - there have been several discussions about GPL licensed code in extensions but it looks like none of that made it into the wiki.  In fact, reading these pages now it seems we define these categories but don't say what impact that categorization has on how the extensions are handled - this should be clarified perhaps based on consensus after this thread.

As it states in the Slicer license terms [1] if you contribute code to Slicer itself you cannot include any GPL code and we can't distribute other people's GPL code with Slicer.  If we did, we'd be required to make all of Slicer GPL, and that's not consistent with our long-held goals of making any or all of the Slicer code base easy to use in commercial clinical products (so they can be used to help patients).

There is a valid question about when the GPL license terms kick in when it comes to extensions.  I consider the GPL to be very vague on this point.  Since we make extensions available as a one-click install and the binary package come from the same server where the user obtained Slicer itself, I suppose one could argue they are somehow bundled, but at the same time clearly Slicer doesn't depend on the extension so it would be feasible to just remove any extension that somehow was later claimed to violate the GPL.

My advice would be to avoid any GPL library dependencies in extensions if at all possible.  If you do find that your extension is impossible to use without the GPL code then please make a big note of it in your source code and documentation so that anyone building on the code is aware of the issue.

I think it is clear that if you include any GPL dependencies in your extension then your whole extension must be GPL.  This may or may not be an issue for you but it is worth keeping in mind that you may not want to pay that price just to use a particular library.

I'm curious what other people think (bearing in mind that this topic has been known to trigger volumes of email, so if nobody chooses to respond, that's okay too!).

Hope that helps,
Steve


On Thu, Mar 30, 2017 at 6:41 PM, Juan Carlos Prieto <[hidden email]> wrote:
Dear all, 

I would like to confirm if an extension using software licensed GPL falls into the "Category 2" extension and is compatible with Slicer's BSD license. 

Would the only requirement be that the software package does not compile/link against Slicer's core? 

Thank you in advance, 

--
Juan Carlos Prieto
Research Assistant Professor
University of North Carolina, Chapel Hill. 
phone: <a href="tel:(919)%20843-9497" value="&#43;19198439497" target="_blank">919 843 9497

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