Boosting the Permutation Based Index for Proximity Searching ⋆ Karina Figueroa 1 and Rodrigo Paredes 2 1 Facultad de Ciencias F´ ısico-Matem´ aticas,Universidad Michoacana, M´ exico. 2 Departamento de Ciencias de la Computaci´ on, Universidad de Talca, Chile. karina@fismat.umich.mx, raparede@utalca.cl Abstract. Proximity searching consists in retrieving objects out of a database similar to a given query. Nowadays, when multimedia databases are growing up, this is an elementary task. The permutation based index (PBI) and its variants are excellent techniques to solve proximity search- ing in high dimensional spaces, however they have been surmountable in low dimensional ones. Another PBI’s drawback is that the distance be- tween permutations cannot allow to discard elements safely when solving similarity queries. In the following, we introduce an improvement on the PBI that allows to produce a better promissory order using less space than the basic permu- tation technique and also gives us information to discard some elements. To do so, besides the permutations, we quantize distance information by defining distance rings around each permutant, and we also keep this data. The experimental evaluation shows we can dramatically improve upon specialized techniques in low dimensional spaces. For instance, in the real world dataset of NASA images, our boosted PBI uses up to 90% less distances evaluations than AESA, the state-of-the-art searching al- gorithm with the best performance in this particular space. Keywords: Permutation based index, Distance quantization, Proximity search- ing 1 Introduction Nowadays, similarity searching has become an important task for retrieving ob- jects in a multimedia database; with applications in pattern recognition, data mining and computational biology, to name a few. This task can be mapped into a metric space problem. A Metric Space is a pair (X,d), where X is a universe of objects, and d is a distance function d : X × X → R + ∪{0}. The distance function is a metric if it satisfies, for all x, y, z ∈ X, the following properties: ⋆ This work is partially funded by National Council of Science and Technology (CONA- CyT) of M´ exico, Universidad Michoacana de San Nicol´ as de Hidalgo, M´ exico, and Fondecyt grant 1131044, Chile.