Sorry for bumping this discussion thread this late, but I discovered the
Berkeley DB license* ("the BDB") and it made me think about what had
been said here.
Haven't looked at the BDB before, and I find it interesting. Taking into
account only the numbered points, it might be the shortest example of a
copyleft license in use in the field, even close to the shortest
possible. It's close in form to a BSD-like license plus source requirement.
The FSF claims that the BDB is GPL compatible, I assume because it does
not specify anything outside the bare minimum, in particular does not
restrict any "further restrictions". Does it even propagate a guarantee
of the four freedoms to modified versions of the software?
On 2012-10-12 13:45, Bradley M. Kuhn wrote:
Mike Linksvayer wrote on 9 August:
> there are cases where unambiguously MPL code could be included in a
> copyleft-next project, if only copyleft-next allowed for it.
Honestly, I'm not convinced that a truly strong copyleft can allow
unilaterally inclusion of other copylefted code -- even weak -- without
bilateral compatibility clauses. We have to consider that such
provisions while seemly safe on the surface may actually be manipulated
to undermine the stronger copyleft by enterprising defense attorneys.
Is the BDB a counter-example to your thesis? Or is it not "truly strong"?
It seems to me that any license, that accepts whatever added conditions
another license contains, will be forward-compatible with the more
restrictive license. Either by enumerating certain allowed further
restrictions, like the GPLv3 vs the AGPLv3, or by not explicitly
forbidding any, like the BDB.
The point about using a weaker license to undermine a stronger one
stands, whether if it means using a weaker, forward-compatible license
to gradually rewrite the code base, or if it means some currently
unknown license jujutsu.