Conflict between vBulletin's license and GPL packages/plugins?

[ElfMage]

(Moderators: please move this thread to the appropriate forum if needed).

I have a question for the vBulletin community at large regarding licensing issues between vBulletin + bridges + CMS/Blog packages (or any GPL package).

I am writing a 'bridge' between vBulletin and MediaWiki (https://vborg.vbsupport.ru/showthread.php?t=123273). While doing so, I started researching portals to use in my site (www.luxurywiki.com), and found that some CMS packages are licensed under GPL (e.g. Drupal, E107) and some under LGPL (e.g. Bitweaver).

So, I tried to learn about this and find the implications of writing an 'extension' (plugin) for MediaWiki, which is licensed under the GPL, that would integrate MediaWiki with vBulletin. vBulletin is a commercial software package, copyrighted by Jelsoft, and licensed on an individual basis to the users who purchase such license (this is my understanding).

In this FAQ about GPL: http://www.gnu.org/licenses/gpl-faq.html#GPLAndPlugins; it is stated that if I write an extension (plugin) for MediaWiki, I have to release it under the GPL due to the fact that MW is loading the plugin dynamically and the plugin uses other MW's internal data structure. (I intended to GPL my plugin).

But, according to the GPL, a GPL licensed piece of code cannot rely on another program/library that is not free (GPL or compatible license).

So, I find myself puzzled by the whole situation. MW is GPL, any plugin I write has to be GPL, but this in turn cannot rely on non-GPL proprietary software (i.e. vBulletin).

Am I misinterpreting something here? Does this make any sense? If any of you have any idea please chime in.

(BTW, as you may surmise, I am not a lawyer :))

[SaN-DeeP]

Can I write free software that uses non-free libraries?
If you do this, your program won't be fully usable in a free environment. If your program depends on a non-free library to do a certain job, it cannot do that job in the Free World. If it depends on a non-free library to run at all, it cannot be part of a free operating system such as GNU; it is entirely off limits to the Free World.
So please consider: can you find a way to get the job done without using this library? Can you write a free replacement for that library?

If the program is already written using the non-free library, perhaps it is too late to change the decision. You may as well release the program as it stands, rather than not release it. But please mention in the README that the need for the non-free library is a drawback, and suggest the task of changing the program so that it does the same job without the non-free library. Please suggest that anyone who thinks of doing substantial further work on the program first free it from dependence on the non-free library.

Note that there may also be legal issues with combining certain non-free libraries with GPL-covered Free Software. Please see the question on GPL software with GPL-incompatible libraries for more information.
Some more information from same page.. It is little complicated...

[amykhar]

You CAN write code to integrate with vbulletin without using any of Jelsoft's files or functions. The data in the database can be accessed using normal php database functions instead of the wrapper class that Jelsoft provides. It's not as easy. It's not as easy to read. But, it can be done if you really want to go the GPL route.

[ElfMage]

Some more information from same page.. It is little complicated...
I interpreted this part as applying to a new project (that needed to use a non-GPL library), not merging two existing projects (one of them already released under GPL). I may be wrong.

You CAN write code to integrate with vbulletin without using any of Jelsoft's files or functions.
This is true, but I would still be using the 'data structures' from Jelsoft's software (SQL Tables). Also, in order for the plugin to be GPL-compatible, it cannot depend on any non-free software being installed (which the plugin would, since it would expect vB's tables in the DB).

Now, realize that I don't want (or need) to release the plugin under GPL (I could always use my own license, free disty or otherwise), but my interpretation (which is one of the main questions) tells me that any plugin for MediaWiki (or Drupal, Xoops, E107, Joomla, etc) has to be GPL (or GPL compatible).