HRG: A Graph Structure for Fast Similarity Search in Metric Spaces

Abstract

Indexing is the most effective technique to speed up queries in databases. While traditional indexing approaches are used for exact search, a query object may not be always identical to an existing data object in similarity search. This paper proposes a new dynamic data structure called Hypherspherical Region Graph (HRG) to efficiently index a large volume of data objects as a graph for similarity search in metric spaces. HRG encodes the given dataset in a smaller number of vertices than the known graph index, Incremental-RNG, while providing flexible traversal without incurring backtracking as observed in tree-based indices. An empirical analysis performed on search time shows that HRG outperforms Incremental-RNG in both cases. HRG, however, outperforms tree-based indices in range search only when the data dimensionality is not so high.