KDE and Qt

• The name of the software is the K Desktop Environment, called KDE for short. It is a graphical user interface that is popular on Linux and other flavors of the UNIX family of operating systems. Virtually all graphical interfaces in the UNIX family are built on top of the X Windowing System.
• The X Windowing System gives the graphics its portability across many systems; the Qt library of graphics objects provides the basic building blocks of an application; and the KDE library provides a standard look and feel.
• When you write a KDE application, you are writing code that will rest on top of a lot of other code. Most of the detailed work of getting your application written has already been done, and that work resides in the libraries of code that will link to your application to do the things you would like for it to do. The diagram in Figure 1 should give you some idea of the levels of software that make up a KDE application.

  Figure 1: The levels of software for a KDE application in Linux.

  
• The way the diagram is drawn makes it appear that the levels are completely separate, but that's not the case. For example, perfectly valid calls are made from KDE classes to glib functions, and there is nothing to prevent your application from making calls directly to, say, glib or the system calls.
• An application typically uses classes from both KDE and Qt. However, the calls are only downward - for example, no part of the Qt API makes use of anything in KDE.