From the framework point of view, data flowing to and from a TCAD tool has to consist exactly of those data components which are ``understood'' by the individual tool. From this viewpoint, existing conventional tools (non-FCTs) can be integrated by wrapping the tool, i.e. by providing a data front and back end converter between the data level representation of the framework and the tool's native data format. All these requirements have been analyzed in the previous section; for the tools there is no difference then between running standalone or inside the framework.
Tools integrated tightly into the framework (FCTs), however, may need further information passed between the tool and the framework. In contrast to a wrapped tool, which, once it is started, runs until its termination uninfluenced by the TCAD system, the tightly integrated tool may interact during run time with the system, or - put in other words - it runs under close control of the TCAD shell. Such a tool will use the data level's error and message reporting facilities, will allow temporary data to be examined during its run, may be stopped and continued by the TCAD shell, and may in turn break and report this fact to the TCAD shell which will have to react accordingly. As far as tool control is concerned, the TCAD shell has to provide the appropriate functionality, but the data and message passing mechanisms have to be provided by the data level of the TCAD system.