support requirement

[VAB]

bruce at perens.com wrote:
> 
> For the vendor it's really a choice of "go Open Source or lose _everything_".
> If you GPL your product, you can probably still make money from it using
> commercial licenses. If someone else clones your product, it's GPL-ed
> anyway, plus you have a new competitor who wouldn't have been there
> otherwise.

Could you explain this to me bruce?  I find it confusing.  I've been 
wondering about dual licensing for some time now.  The example that
brought it to my attention was the PHP licensing.  PHP consists of
an interpreted programming languages (much like perl), and a run time
for that interpreter.  When you download PHP from www.php.net you are
allowed to choose between the GPL and a less restrictive license
written by the PHP programmers which allows commercial forking.  What
position does this put the PHP programmers in?  Are they allowed
to pick up code from the community (GPL'd code) and include it in
PHP from which it can then propagate to commercial forks of PHP?
I've seen many other people do dual licensing with supposedly "GPL"
compatible licenses such as the artistic license as well.

Am I mistaken and this type of dual licensing is only possible 
with an original work which contains no previously GPL'd code?
I had thought that this would be the case based on my reading 
of the GPL, but I have a hard time believing that all of the
code dual licensed out there is original code.  Will it satisfy
the GPL's viral clause (Paragraph 2b) to have the code licensed
by multiple licenses and at least one of those licenses be the
GPL?

Is there a way I can prevent this from happening to my software?
Is it legally possible for me to write a license that restricts
any one at any time in the future from dual licensing any of the
code that I write and taking it away from the community?

	- VAB
---
V. Alex Brennen    [vab at pog.ufl.edu]
[http://www.metanet.org/people/vab/]
Systems Administrator/Sys. Prgr
Pediatric Oncology Group
[http://www.pog.ufl.edu/]
Statistical Office
University Of Florida
352.392.5198 x303
352.392.8162 Fax