Create migration from existing database

I'm looking to see if anyone knows of a tool that can be used in ruby
to autogenerate a rails migration
from an existing database that comes from a non ruby project. I know
I can do this with rake db:backup with a rails project, but does
anyone know if its possible outside of this realm. I looking to build
a project to migrate a database from one platform to another. Say
Oracle to MsSQL server. Migrations would help immensely with this
concept, but can these be generated and not have to be built?