Java Data Objects and automatic schema migration

[Rob]

Does there exist a tool or facility in jdo which will allow you to
automatically migrate a schema based from the .jdo files? For example
suppose I have a class called Foo with integer fields bar and baz and
a metadata file that describes that and a table in the database that
mirrors the java class. Now, let's say that I add a field to Foo
called bim and make the appropriate additions to the metadata. Is
there a tool that I can use to generate the DDL which would alter the
Foo table in the database to match Foo v2.0? What about the DDL
necessary to roll back?

Thanks for your help,
Rob