Fast searches and query operations in high dimensional databases require efficient index structures. Amonga variety of index structures, the index structures in metric spaces are very useful. They can be used in an extensivefield, such as searching for protein molecular chains with certain sequences in Computational Biology and matching agiven strings fuzzily in Text Retrieval. In this paper, the features of index structures in metric spaces are analyzedand subsequently a further classification is given to these index structures. Finally, some representative index struc-tures are introduced in detail.
