Understanding MPL

Ciaran O'Riordan ciaran at fsfe.org
Wed Oct 1 23:11:45 UTC 2008

The MPL is often called a file-level copyleft licence.

I haven't read the MPL in years, but a summary I heard from a reasonable
person is that if you make changes in the files you received, you have to
keep the same licence that whole file.  But if you make some changes to
existing files, and add your own new files, then you can freely choose the
licence of your own new files.

"gk at fsfe.org" <gk at fsfe.org> writes:
> (1) Does that mean, that as long as somebody does not use lines from a
> file of the Covered Code, he may distribute his proprietary code, which
> calls functions of the Covered Code, in a single executable?

By what I wrote above, yes.

> (2) Only when he alters the Covered Code, or uses portions of it in some
> other file, that code would be under the Terms of the MPL?

By what I wrote above, yes.

> (3) That would be similar to the LGPL, right?

The MPL is much weaker than the LGPL.  All changes to LGPL'd software has to
be released under the LGPL - even if the changes are in a separate file, if
they form part of the thing covered by he LGPL, then they have to be LGPL'd.

Only things that could reasonably work without any of the LGPL'd code can be
considered separate and not bound by the LGPL.

The LGPL also has good safety features to ensure that when someone receives
a combination of LGPL'd software and proprietary software, the user can get
everything necessary to modify the LGPL'd part and recompile the whole.

> (4) What about deriving a - for example Java - class from a class under
>     (a) MPL
>     (b) LGPL
> Would the derived class be allowed to have a proprietary license?

I don't know the Java language, so I don't know what "derive" means in that
context.  So I'll go for: Maybe :-)

There might be some helpful info here:

CiarĂ¡n O'Riordan, +32 477 36 44 19, http://ciaran.compsoc.com/

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