My current project is developing rapidly so I wondered how other
developers handle generating the script to do each upgrade.
I can compare the ddl using dev studio or db workbench to get a
starting point and then hand modify but this is very time-consuming
and requires having handy a copy of the previous database and data
files, is there something better out there that I have been unable to
find?

This is on a fedora core 8 platform using firebird 2.1.1 if that makes
a difference