3.2.1 Client-Server Approaches

Fig. 3.3 shows the conceptual view of a client-server approach. The client application connects to a server via a procedural interface and does all data access and manipulation queries through calls to procedural interface routines. The server internal data structures are totally opaque to the application. In fact, concentrating on a standardization of the procedural interface definition allows different server implementations to be made with different internals and thus varying performance when applied to certain TCAD problems. So, one server might perform well when confronted with unstructured grid manipulation, while another server might exceed in complex geometry operations.

  
Figure 3.3: Conceptual view of the client-server approach

A recent client-server approach is the SWR 1.0 specification of the CFI/TCAD TSC [Yang94][SWRI92][SWRD92][Boni92a], defining an object-oriented application interface for TCAD data access. The Semiconductor Engineer's Workbench (SEWB) [Dutt93] from Stanford University uses this client-server specification together with the ACIS solid modeller for geometry manipulation. Visualization is done through the HDF-VSET visualization format [Bish92] using the AVS scientific visualizer [Upso89][Star91].

Although the client-server approach looks intriguing, there are major conceptual drawbacks involved in its design:

• Standardizing a procedural interface is dangerous for all TCAD tools which are not explicitly designed to work with this interface, since the interface specification has to define which data structures are to be and how they are used in communicating with the server. If those applications are forced to use the conceptually different (because often object-oriented) data structures of the server procedural interface, considerable effort has to be undertaken to write interface modules for application-internal translation of these data structures, often resulting in severe performance and storage consumption drawbacks. Therefore most implementations are going to isolate those applications through a wrapper - again an approach which is not necessarily desirable, as already discussed in Section 2.1.1.

• It is questionable, if a true client-server architecture using the network will exhibit the required performance in a TCAD environment, since large data amounts like grids, attributes or solver stiffness matrices (especially in 3D) have to be communicated between client and server. Although mapping client memory into the server substantially improves performance, this approach is neither portable nor does it work over the network.