Activity Backward Compatibility (was re: Re: joyride 2128 smoketest)

[Daniel Drake]

On Mon, 2008-07-14 at 09:14 -0400, Greg Smith wrote:
> - Leaving aside how its done technically, I believe that Linux 
> distributions are fully backward compatible. That is, you can go to the 
> latest supported Distribution and leave your Firefox (or any 
> application) on its older release and it will still work fine. Let me 
> know if that is not correct. I think that is what we need to strive for, 
> eventually.

"Upgrading a distribution" is a very broad thing indeed. There are many
components and considerations involved.

I'm unable to think up any specific examples, but in general I think I
disagree with your statement. Software that runs on one version of a
distribution will be dependent on components which get upgraded/removed
during the distribution upgrade, so in the end that piece of software
will end up not working.

The way that distributions get around this is by upgrading everything at
once. In your example, staying with the old firefox would result in a
broken firefox, but the distro upgrade software would make sure that it
updates firefox to one compatible with the new distro components. You
might not realise that Firefox got upgraded, it might look and feel
identical to the old one, but it did.

This is possible for distributions because both firefox (the
application) and it's dependencies (underlying libraries etc) are all
under control of one entity: the package manager. This isn't true in our
case, where libraries are controlled by the rpm/yum package manager, but
applications (activities) are not.

Daniel