title: xhange classes attributes in existing db4o in android
body: <p>I'm considering to use db4o in my android project to store objects but my concern is if in the future I want to change one of the objects attributes how do i deal with the existing data of that object in the db4o file? I know in sqlite3 environment this can be done by altering the table structure in the onUpgrade() method, so how does db4o deal with this?</p>