I'm a little confused as to licensing requirements regarding a plugin I've been developing. Here's the situation of what's involved:
1. My company has an existing, stand-alone webapp under a proprietary license which allows free use for non-commercial purposes, but requires a non-free license for revenue-generating use. The webapp itself uses no open-source code (in fact has a GPL-incompatible license) and the interface is a simple HTML template.
2. The plugin acts as a "bridge" between WordPress and the WebApp. The plugin, of course, uses core WordPress code and will be released under the GPL.
3. The plugin and the WebApp are not bundled together. The plugin has a "convenience" option to download and install the WebApp to the server, or a user could download it and install it manually. Once installed the WebApp is actually a standalone program still capable of displaying its own content in its own templates.
The plugin essentially consists of two php files - one for the back-end admin and another acts as a "template" file (though technically not a WordPress template file) that is basically a php version of the WebApp's HTML template.
It is in this template that the actual "bridging" occurs - it contains WP core code to pull content from the database but it also pulls in the scripts and stylesheets from the WebApp installation on the same server. The template page and database content can technically be viewed without the WebApp's code (if you were to disable scripts and styles), and the WebApp's scripts and styles exclusively manipulate only the database CONTENT, which (according to what I've read) is NOT subject to the WordPress license.
Someone to whom I was talking about this suggested that, since the plugin is mostly useless without the WebApp, and they must both be installed on the same server (and it doesn't matter if I don't ship them bundled together), they form a "combined program" that is ALL subject to the GPL, rather than the exception for a bridging plugin to a "web service" that exists in another address space.
My interpretation, though, is that while the plugin must be released under the GPL because it uses core WP code, the WebApp is not subject to the GPL because it uses no such code and only interacts with content, which is also not subject to the GPL. That the WebApp needs to be installed on the same server as WordPress (and the plugin) does not automatically "combine" them, therefore they are simply "aggregated" on the same server as independent programs with no licensing cross-pollination. Furthermore, the "bridging" is done in the template via standard HTML script and link tags, which I don't believe are considered "dynamic linking" methods under the GPL. And lastly, it is conceivable someone could modify the plugin template to include their own scripts and styles instead of using the WebApp's (I'm just hoping they won't want to).
I'd ultimately like to submit the plugin to the WordPress repository, but I'm unclear if it technically meets the licensing requirements because of what it is and how it works.
Is this plugin project a non-starter, or am I ok with the GPL when I'm just bridging WordPress content to a proprietary web application installed on the same server?