This week's book giveaway is in the OO, Patterns, UML and Refactoring forum. We're giving away four copies of Refactoring for Software Design Smells: Managing Technical Debt and have Girish Suryanarayana, Ganesh Samarthyam & Tushar Sharma 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.