I finally found a really useful working paper and law review article written by some European open source attorneys and the Free Software Foundation Europe on linking issues and the GPL license. I thought I would share some of the highlights with you as it is really hard to get some good practical guidance on open source legal issues. As a bonus, this perspective tries to marry the legal analysis with the technical analysis. Take a read!

(1) Derivative Work or Compilation (copyleft obligations)

• Static Linking (GPL’d code combined with your code in one executable at build time)
• Macro/Template Expansions (embedding GPL’d code into your code)

(2) Close Call (aka, it depends)

• Plug-ins (to extend functionalities of other programs)
  • depends on external factors (I added a few of my own here):
    • dependency/independency of your code;
    • communication protocols/sharing resources;
    • copying of API host code/no copying of API host code;
    • core functionality not subject to copyright/functionality subject to copyright; and
    • existence of other libraries with the same function.

(3) Independent and Separate Program (no copyleft obligations)

• Dynamic Linking (calling and using library only at run-time; (no GPL code copied, modified, translated or changed . . . I added this part from Larry Rosen’s view (see below) on it))
  • remember to look at the above external factors as it could become a derivative work if the facts change
  • oh yea, I moved Dynamic Linking to this section as I think it fits in here more than Close Call
• Interprocess Communications (remote procedure calls)
• System Calls (core operating system resources)
• Interpreted Language ‘Scripts’ (not compiled, executed by interpreter, no third party code incorporated)

So long story short, this is an evolving issue and I don’t think the definitive work has been written, but don’t let that stand in your way of learning more about it. As an open source attorney and proprietary software attorney, I thought you should be aware of this, as these folks did a fantastic job with this working paper and law review article (see below).

Resources:

Working Paper on Software Interactions and the GNU Public License (July 2010)

Brian, Malcolm (2010) ‘Software Interactions and the GNU Public License,’ IFOSS L.Rev, 2(2), pp 165-80

Larry Rosen’s view on Dynamic Linking.

Disclaimer:

This post is for informational and educational purposes only, and is not legal advice. Hire an attorney if you need legal advice.