For all batch mode applications (these are applications that do not require user interaction) the task level integration and the presentation integration (according to [56] and [58], that is the provision of applications with a homogeneous user interface) are accomplished within a single context. LISP functions are used to create a layer of virtual applications on the task level for one or more physical applications (executables). Figure 4.1 shows two characteristic examples.
Figure 4.1: A set of physical applications is mapped to a set of virtual
applications on the task level. The user interface for these
virtual applications is implemented in the task level programming
environment, leaving the physical applications entirely unaffected.
A typical example for a one-to-many mapping (``Application A'' in Figure 4.1) is a device simulator, where for every desired type of device characterization a function that performs the required simulation step and extracts the requested parameter is implemented (``Virtual Applications W'' and ``X'' in Figure 4.1). For process simulation the situation is inverted. Several physical applications are run consecutively under control of a single presentation (VISTAs Simulation Flow Controller [86]). Again, the mapping is done in the task level environment, using the notion of virtual applications.
Note that this feature is only possible with a dedicated task level that separates the applications from the presentation level (each application containing its own presentation would prevent the ``virtual tool'' features). This is one of the most important features for supporting non-expert users. The intermediate task level layer allows the user interface to be tailored to design tasks instead of application peculiarities.
Compared to the types of tool integration according to Wasserman [56], the task level integration of VISTA resembles to a certain extent the combined process, control, and presentation integration.