2.4.3 Qualitative Functional Requirements

Application Framework Architecture.

It should be clear from preceding considerations that an application framework architecture is optimal for any large CAD system.

Data Level.

The spectrum of computational models and methods used in Technology CAD is impressive. It ranges from analytical models for device characterization or response surface modeling to multidimensional attributes defined on complex spatial grids, from polygonal geometry representations to cellular automata for topography simulation.

This variety of methods is a curse on the data level of an application-framework. The data level must be generic enough to accommodate all required (sometimes even competing) representations of device structures and other design data. Due to the different abstractions employed in physical modeling semantical ambiguities in the interpretation of these data must be anticipated.

Moreover, as simulation methods change and physical models are becoming more comprehensive, additional information must be stored and exchanged between applications, so that good extensibility is a major requirement for the data level.

Task Level.

The task level implementation must offer facilities for task and flow definition and allow for the control and sequencing of a variety of tools. Requirements are discussed in detail in Section 4.1.

Presentation Level.

With all due right, Technology CAD users nowadays expect a comfortable presentation of the services provided. These expectations include a homogeneous intuitive graphical user interface for the data level, the task level, and for all integrated applications. One may apprehend a certain gap between the demand for ease of use and the semantical complexity of TCAD tasks and tools that are represented. The fundamental de-facto standard for the presentation level of application-frameworks is the X Window system [55]. Detailed requirements will be given in Section 3.1.

Integration and Development Support.

For most practical Technology CAD problems a combination of several single applications is used. These applications may exhibit entirely different properties. Some are available in source code while others are only licensed for a given workstation, some are coded in FORTRAN using binary output formats while others are coded in C running on ASCII input and output files. A framework must hence not only allow for tool integration using strict interfaces, but actively support and facilitate tool integration by offering a variety of ductile (nevertheless well-defined) interfaces and integration mechanisms. The modularization of existing applications and the development of new applications must be supported within the framework.

Generic Services.

A significant amount of TCAD methodology is fairly technology-independent. This functionality may be provided by framework services. Examples include CASE tools for application development, scientific visualization, structure editing facilities, grid generation, interpolation, and many more.