LDC: enabling search by partial distance in a hyper-dimensional space

Recent advances in research fields like multimedia and bioinformatics have brought about a new generation of hyper-dimensional databases which can contain hundreds or even thousands of dimensions. Such hyper-dimensional databases pose significant problems to existing high-dimensional indexing techniques which have been developed for indexing databases with (commonly) less than a hundred dimensions. To support efficient querying and retrieval on hyper-dimensional databases, we propose a methodology called local digital coding (LDC) which can support k-nearest neighbors (KNN) queries on hyper-dimensional databases and yet co-exist with ubiquitous indices, such as B+-trees. LDC extracts a simple bitmap representation called digital code(DC) for each point in the database. Pruning during KNN search is performed by dynamically selecting only a subset of the bits from the DC based on which subsequent comparisons are performed. In doing so, expensive operations involved in computing L-norm distance functions between hyper-dimensional data can be avoided. Extensive experiments are conducted to show that our methodology offers significant performance advantages over other existing indexing methods on both real life and synthetic hyper-dimensional datasets.