View Materialization Techniques for Complex Hierarchical Objects
In many design applications, it is common practice to store corn-pfex hierarchical objects in a compactfolded form to save storage space and to reduce processing costs for accessing the objects. In these folded representations, complex objects are built up from identical and otherwise indistinguishable objects. Howevec it is o&en necessary, especially during the refinement of data, to distinguish between these identicul forCtd objects by personakkg a subset of them. The established practice is IO eqficitfy unfold the hierarchical objects and thus create space in which to store distinct personalization data for each object occurrence. However, this explicit unfolding is costly and time consuming, resulting in a potentiaZfy much larger structure, and substantially increasing the costs of querying and updating the design. Therefore, we propose an unfold operator that supports access to data in a virtua& Unfolded view. We describe how to updare customized values for each hierarchical sub-object through the unfolded view. We propose alternative strategies for the maintenance of personalization values, representing various portions of the view materialization spectrutn. We present a performance evaluation comparing these strategies as well as the traditional explicit unfolding approach.