Round-trip engineering as applied to a database means reverse engineering (database to data model) and forward engineering (data model to database) back and forth.
In this article, Djoni Darmawikarta shows how to maintain an existing MySQL database using Power*Architect. Particularly, he shows by examples, how to reverse engineer an existing MySQL database, update the resulting data model, compare the updated model with the ‘old’ database, and implement the updates by forward-engineering them back to the database.

Mas:

http://www.packtpub.com/article/database-data-model-round-trip-engineering-with-mysql