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Re: GPL confusion

From: Martin Dickopp
Subject: Re: GPL confusion
Date: Sat, 22 May 2004 00:26:08 +0200
User-agent: Gnus/5.1006 (Gnus v5.10.6) Emacs/21.3 (gnu/linux) writes:

> I'm trying to wrap my non-lawyer brain around the GPL. In particular
> I'm not clear on what 'based on' means (as regards whether a project
> is derived from a GPL'd project or not). Particularly I'm trying to
> understand at what point the project I'm making is required to be GPL.
> Here's a specific scenario:
> I decide to make a Widget Tracking program. It provides all sorts of
> useful views on widgets - who ordered them, what subwidgets they're
> made of, etc. Standard data-miner app.
> Suppose I want to use MySQL as a database under MySQL AP's GPL option.
> Does merely using it as a database invoke the GPL requirement on my
> Widget Tracker app? 

That depends on the details of how you use MySQL.  A good rule of thumb
is to ask yourself the question: Can you write your program without
downloading MySQL first, i.e. is reading the MySQL documentation enough
to make your program communicate with MySQL?  If the answer is yes, your
program is clearly not based on MySQL.  If the answer is no, this is a
strong indication that your program is indeed derived from MySQL.

> Right now, as I interpret the license it does. So let me proceed
> further on that assumption:
> Suppose I define an interface for accessing WT (Widget Tracker) data
> and provide one or more out-of-the-box implementations for it, ie:
> file-based (text, xml, etc), ODBC compliant (or JDBC), and/or a MySQL
> implementation.
> Sticking to the GPL MySQL scenario, can I GPL just the class that
> implements my db interface for MySQL and make it (incl its source &
> the GPL license) separately downloadable/installable from the main
> Widget Tracker app?

If your program is based on a GPL licensed work (for which you don't
hold the copyright yourself), you have to license your complete program
under the GPL.  However, if you write /two/ similar programs, one which
is based on MySQL (i.e. the Widget Tracker which uses MySQL) and one
which is written by you alone (i.e. the Widget Tracker which uses
file-based storage), you can license the latter under any terms you
want.  The fact that the two programs share most of the code (i.e. the
Widget Tracker code) is not a problem, as long as you hold the copyright
to the shared code.


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