The GNU Public License

By Michael Kay on June 07, 2009 at 02:18p.m.

I've been thinking carefully about whether there's a way to reduce the number of people "freeloading" on the back of Saxon - that is, selling commercial software that relies heavily on Saxon functionality without contributing anything in return. One potential way of doing that is switch in some way to a dual licensing approach: make application vendors choose between paying for a commercial license, and using the product under the GPL (GNU public license), which prevents them from creating "derivative works" unless those works are also licensed under the GPL (that is, made available as open source products). This is essentially the way MySQL works, and it seems to work well for them.

However, there seem to be two obstacles in this approach that are very hard to overcome.

The first is that the language of the GPL is very vague, and as far as I can see, it doesn't do what it claims to do.

It's often thought that GPL says that if program A links to program B, and program B is issued under the GPL, then the GPL also applies to program A. Well go and read it: that's not what it says. GPL (this applies to both v2 and v3) doesn't even use the word "linking". It speaks of a "derivative work under copyright law: that is to say, a work containing the Program or a portion of it". If someone distributes an application containing calls to Saxon, and tells you to download Saxon from SourceForge, I don't see how anyone can claim that the application is a derivative work under copyright law. It would be like saying that I've created a derivative work to Harry Potter merely by encouraging you to get yourself a copy and read it.

Now you'll find plenty of statements like "It has always been the FSF's position that dynamically linking applications to libraries creates a single work derived from both the library code and the application code." Well, that may be their position, but it's not what the license says. And how can it possibly be true? The dynamic linking is done by the user, not by the supplier. If someone writes an application that calls JAXP interfaces, does that make the application a derivative work of every XSLT processor that implements JAXP interfaces, even XSLT processors that haven't been written yet? The idea is absurd.

The other major obstacle to using the GPL is more of an ethical point than a technical or legal one. The GPL license requires you to sign up to a world view which I simply don't share. The preamble says, for example "the GNU General Public License is intended to guarantee your freedom to share and change free software--to make sure the software is free for all its users." Well, sorry, that's the opposite of what I want to achieve. I think it is right in principle that those who get benefits from software should contribute to the cost of its creation. My only reason for even looking at the GPL is to achieve greater fairness in this regard: essentially, to encourage those who get commercial benefits from using the software to pay for a commercial license.

The Free Software Foundation includes in its FAQ statements like "If you hope some day to look back on your career and feel that it has contributed to the growth of a good and free society, you need to make your software free." I disagree 100% with that: I have spent 25 years of my life producing commercial software and I think that software has contributed just as much to society as the free software I have produced. There are things I dislike greatly about the capitalist system, for example the incredible waste of resources that goes into the unproductive activities of advertising and marketing, but (unlike the FSF, it seems) I do not disagree with the principle that those who produce useful things should be rewarded for their work. And I really don't want to sign up to a license that asks me in its preamble to agree with a political and philosophical position which I don't hold.

This leaves me with the problem I started with of course: is there anything I can do from a licensing point of view to achieve my objectives, having ruled out GPL. On the other hand, MySQL must be doing something right.