Two compatriots and I have been developing a web app and now have the happy problem of needing to migrate existing customer data to the data model of a new version. We've been using EJB annotations since doing so lets us spend the bulk of our time working on the value-add pieces of the application and only deal with mapping objects to the database at a relatively high level.

Now we're embarking on the next version of the product, and expect to deal with migrating existing customer's data. While we're capable of writing the SQL to munge the database as needed, we'd rather find some framework, tools, or methodology to help us make the transition. Has anyone else run into this issue?