An Estimating Model Of Node Accesses For Inn Search Algorithm In Multidimensional Spaces

Nearest Neighbor (NN) search has been widely used in spatial databases and multimedia databases. Incremental NN (INN) search is regarded as the optimal NN search because of the minimum number of node accesses and it can be used no matter whether the number of objects to be retrieved is fixed or not in advance. R*-tree is still regarded as being among the best high-dimensional indices. This paper presents an analytical model for estimating performance of the INN search algorithm on R*-tree. For the first time, our model takes m (the number of neighbor objects reported finally), n (database cardinality) and d (dimensionality) as parameters, focusing on the number of node accesses. In our model, (1) the two key factors of d(m) (distance from the m-th NN object to the query point) and ah (side length of each node) are estimated using their upper bounds and their lower bounds, which is very helpful to effectiveness of our model; (2) the particularity on the number of entries in the root node and the possible difference of fanouts between the leaf nodes and the other nodes are taken into account. The theoretical analysis is verified by experiments.