I have the tutorial working which has been a great help in understanding how to use ObjectDB.
I have found one problem. The database file (C:\glassfish3.1\glassfishv3\glassfish\domains\domain1\eclipseApps\Guestbook\WEB-INF\db\guests.odb) is reset on occasions; I am not sure what set of events causes this.
I can enter a number of entries, stop Glassfish, use the Object Explorer to view the objects. At some point, may be when restarting Glassfish or re-publishing the application, the database is empty.
Any help would be much appreciated.