Qddb provides several generic (that is, application-independent) interfaces. You don't have to design your own custom user interface in order to use a new relation. Once you become expert, if you enjoy programming, you will be able to build custom interfaces yourself.
Qddb provides both text-based and graphical generic interfaces. The text-based interface (primarily qadd and qedit) allows you to add, modify, and search for data with your favorite text editor. The graphical interface nxqddb, designed to use the X Window System, makes it easier to select and modify existing tuples.