This week's book giveaway is in the OCMJEA forum. We're giving away four copies of OCM Java EE 6 Enterprise Architect Exam Guide and have Paul Allen & Joseph Bambara on-line! See this thread for details.
Not sure what you want to define here: columnDefinition is, by design, non-portable database specific DDL. The @Column annotation has a few attributes, for example, length, that you can use for portable customization.