As the central coordinating instance,
the task control layer
takes care of controlling all activities
initiated via the GUI, the ASCII interface, or a batch
file.
It is implemented as a set of dedicated VLISP functions
and establishes object-oriented interfaces for all task-level
services.
The VLISP shell interpreter - not shown in the figure -
provides the basis for the
implementation of all other internal modules.
It provides interfaces to the operating system, the
graphical user interface (GUI),
and the PIF Application Interface (PAI) [FFS
91]
to conveniently access simulation data stored in the Profile
Interchange Format (PIF) [Duv88].
All operating-system dependent
services are encapsulated by the VLISP interpreter , which ensures
portability over a wide variety of operating systems and platforms;
see below in Section 3.6 for more details.