We have a traditional fat client application (currently 10.2B). A lot of the newer code is N-tiered but we don't currently use Appserver at all.
1 - Assume we could move to mixed model, i.e. majority of the application still runs fat client, but selected processing could be executed via an appserver ?
2 - Licensing: apart from purchasing the appserver licenses, would additional database licenses be required for each appserver license ? Obviously the fat client would have it's own client networking/database license.
1. Yes you can have some part of your app still running "fat client" and others using the AppServer.
2. Except the AppServer license, you'll not need additional db licenses.
And if I may suggest, you should really look into upgrading to OE11.5 and user our new AppServer. Here is a link to a recorded presentation about new features in OE11.5. Hope it help.
We are definitely looking at moving to 11.5 and the new appserver.
By the way, here is another link to the OE11.5 new AppServer documentation, just in case