Mapping a Version Model to a Complex-Object Data Model

Support for version management of highly interconnected complex objects is a strong requirement for database systems supporting CAD. In this paper, we present such a version model and exemplify it by means of the VLSI design process. However, we are not only interested in the version model itself, but also in its implementation on top of an existing complex-object data model without version support. In contrast to similar solutions basing on the relational data model, this approach allows for a simple and efficient implementation of the version model, allowing for powerful retrieval operations. Sharing of data, which occurs necessarily among versions, is system controlled. This prohibits redundant storage of data. We conclude that implementing a complex-object database system supporting versions is not more complicated than implementing a complex-object database system without version support. In this paper, we present a version model for computer aided design (CAD) purposes and its implementation on the basis of a complex-object database management system (DBMS). We illustrate the functionality of our model with the help of a VLSI design example, but we claim that it is useful for all kinds of CAD. The VLSI design approach to be considered here is based on the two strategies hierarchical decomposition and step-wise refinement [9]. The latter copes with the development of a chip starting from its behavioral description, passing an structural and an topological description, and ending up with its mask layout. In the structural description, the module (which is a better term than " chip " in this domain) is described as a collection of up to 100 simpler modules and connections among these modules (hierarchical design method). Placing these modules together and generating the corresponding geometrical information leads to the topo-logical description of the module (its floorplan). In this domain , each module is represented by a rectangle. We use the design of a 2-bit adder as a simple example. Figure 1.1 depicts the structural and topological design of a 2-bit adder based on three 1-bit adders and one half-adder. Each 1-bit adder is built up by one AND and one XOR gate. Data modelling Looking at figure 1.1, we can identify three object types, namely Interface, Instance, and Contents as well as three link types among them, namely (Instance) part_of (Contents), (Instance) instance_of (Interface), and (Contents) implements (Interface). This abstract description of the data is basically sufficient from the viewpoint of the structural domain. …