It is striking that hardly a correspondence neither in maturity, nor in architecture, between the data level and the task level of the listed TCAD systems can be found. The variety of task definition, tool invocation, and flow control methods is impressive. However, just a few of the investigated TCAD systems offer a dedicated task level, especially with respect to tool integration.
Statistical simulation and semi-automatic design optimization dominates the flow level of PREDITOR and the Hitachi system. Similar facilities can presumably also be found in the MECCA, VATS, and EASE (FASST/TEL) TCAD systems. It is, e.g., also accomplished in STORM by the NORMAN optimizer [47]. This sequencing by master control applications is not a task level, but is often mistaken for it.
Unix shell based solutions are prevalent in many systems for the sequencing of tools and may be accepted as task level (although they lack portability), when providing a homogeneous, tool-independent environment for task and flow definition (including tool parameters), as in SATURN.
The embeddable command language Tcl[48] is used in MECCA, PREDITOR, VATS (WIZARD), and PROSE. It is very popular and efficient in creating an ``instant'' user interface and extension environment for a given system.
Systems which are close to CIM, like EASE, CAFE, but also a notable process flow validation system [49] from Hitachi, are very much process-flow oriented, so that due to the existence of a process flow implementation (CIM), they have skipped the stage of a distinct, generic task level environment in their evolution.
In most of the existing TCAD systems, however, implicit assumptions about the design flow (cf. Figure 1.1) have had an impact on the structure of the software and restrict design tasks which can be performed or implemented.
A notable object-oriented approach to (Electronic) CAD tool integration and control has been demonstrated in the Cadwell [50] design framework. The system features a blackbord architecture and tools can be invoked in an opaque manner according to the users progress through design space.