MONORAIL: A Disk-Friendly Index for Huge Descriptor Databases

We propose MONORAIL, an indexing scheme for very large multimedia descriptor databases. Our index is based on the Hilbert curve, which is able to map the high-dimensional space of those descriptors to a single dimension. Instead of using several curves to mitigate boundary effects, we use a single curve with several surrogate points for each descriptor. Thus, we are able to reduce the random accesses to the bare minimum. In a rigorous empirical comparison with another method based on multiple surrogates, ours shows a significant improvement, due to our careful choice of the surrogate points.