devaki-nextobjects is not yet another UML design tool. There are some excellents like ArgoUML It just stick to the UML convention in it's paradigm.
Designing database may require several points of view : it is not a database browser, it's not a reverse engineering tool.
It is not an Eclipse plugin. It have never appeared to be neccessary.
It's not a code generator.
As often in the database playground it can't really deal with inheritancy.