If I import my objects from a data dictionary I am able to alter my objects and afterwards synchronize it to my Data Dictionary (database). I am even able to determine another connection to do this synchronization. But if I designed my entire model from scratch, I'm not able to synchronize it to an existing Data Dictionary. I already generated my script and used it to create a new schema, with all my objects in it. Now I need to be able to alter my objects and synchronize it to this existing data dictionary.
you can compare to database using import from dictionary wizard - check "Swap Target" flag if you want to generate update for database. If you import at least one table into model you can use sync functionality. That step won't be necessary in next release.