DO4 still doesn't support mapping for views, even in Legacy mode. Although it's a good idea to implement this ;) We'll think about adding this quickly.

Concerning DO3 databases: as far as I can judge, now it must be possible to map new entities to them in Legacy mode: custom type discriminators are there, so this must work. On the other hand, I'd implement IModule providing values for these type discriminators automatically based on [doSysTypes] table content (or simply adding this info to definitions model).

Summary:

• There is no view support, but we'll consider implementing it in Legacy mode

• Most likely, you already can consume v3.9 databases, but ideally you need a module automating extraction & assignment of type discriminator values.