The term presentation level, although quite common in the CASE area, is less often used in TCAD. It basically denotes a homogeneous user interface. Another established term with more specific semantics is that of GUI for graphical user interface, which is a special (the predominant) case of a presentation level. Most of the GUIs found in TCAD are window-oriented and based on X Windows. In Technology CAD, the presentation level is always strongly coupled to the task level (if one exists).