Improved Methods for Signature-Tree Construction

Signature-based tree structures which have been proposed in the past do not perform well for large databases. The problem arises from the fact that they are incapable of pruning searching, especially at the upper tree levels, and thus they have decreased selectivities. In this paper, we locate a number of reasons for this problem and propose several methods for node splitting and partial-tree restructuring, which lead to improved query-response times. We have implemented all methods and we present experimental results, which indicate that the proposed methods are superior in all cases to the standard one and up to 5-10 times better for medium and higher weights in inclusive (partial-match) queries. Additionally, we have developed new functions for the performance estimation of signature trees which, in contrast to a previous estimation function, are able to take into account the outcome of different split methods and to provide more accurate estimation.