Several workstation-based systems can be found which address the issue of multi-tool integration into a unified user interface, mostly on top of the X Window system. Most of the early systems use an integrating interactive application that provides front- and post-end functionality and also sequences the integrated tools. PRIDE[21], based on Sunview, exhibits a user interface (and task level) architecture which is strongly influenced by the preprocessing - computation - postprocessing flow model of TCAD. SIMPL-IPX[38] directly uses Xlib and features a central interactive graphical editor which has menu-oriented facilities for running simulators.
A more flexible and extension-oriented user interface architecture has been accomplished in PROSE[36] from the University of California at Berkeley and in IBM's WIZARD user interface[12], which is mainly due to the use of the generic Tcl interpreter[48] and Tk toolkit[51].
It may be said that the importance of the user interface design and implementation is severely underestimated and disregarded. This is probably because the user interface is considered an auxiliary second-order component that ``just supports the casual user'', not a critical component of a TCAD system. Only the commercial systems (MASTER and CAESAR) care for GUI functionality and portability (at least across a few UNIX-based Motif and OpenLook environments).