You may never need to write custom Qddb applications. But if you do, we suggest that you consider using the Fx toolkit. In order to program Fx effectively, you need to understand the Qddb extensions to Tcl that allow you to deal directly with schemas, tuples, and the like. This chapter discusses those extensions. Chapter 8 discusses the Fx toolkit itself.
There is a lower level you could use instead, the Qddb C library level. We have implemented such utility programs as qstall, qedit, and qadd on this level. Although the Qddb C library interface is reasonably nice, Tcl and Tk [4] provide a much more convenient ground for applications programming. The effort you need to spend to learn Tcl (if you don't already know it) will be repaid in the ease with which you will be able to write Qddb applications.
The interactive Qddb shells qtclsh and its graphical partner, qwish, provide a set of convenient abstractions accessible through Tcl commands. Any programmer familiar with relational databases and Tcl should have no trouble learning the Qddb Tcl abstractions and commands.