Re: GPL confusion

[Sam Holden]

On Fri, 21 May 2004 17:40:15 -0400, yeah@nothanks.com <yeah@nothanks.com> wrote:
> 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.

The GPL isn't the source of the requirement. Copyright law is.
If copyright law says that a work is a derivative of a GPLd work then
the GPL kicks in.

Copyright lawyers disagree on just what is and what is not a derived
work. Since the copyright holder is the one who can sue you if you
violate their copyright then using their definition of what is derived is
the best way to avoid a lawsuit. 

> 
> 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? 

Talking to the database certainly wouldn't. Using their client library
to talk to the database may make the app a derivative of the client
library. The FSF would hold that it does, for example.

> 
> 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?

I believe so. Even using the FSFs definition of a work being derived from
a library that it dynamically links to it would pass. Since that 
definition only holds when the only a GPLd dynamic library is usable, as
soon as an alternative library is available then the work is clearly not
a derived from one particular library.

-- 
Sam Holden