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In computer science, an X-tree (for eXtended node tree[1]) is an index tree structure based on the R-tree used for storing data in many dimensions. It appeared in 1996,[2] and differs from R-trees (1984), R+-trees (1987) and R*-trees (1990) because it emphasizes prevention of overlap in the bounding boxes, which increasingly becomes a problem in high dimensions. In cases where nodes cannot be split without preventing overlap, the node split will be deferred, resulting in super-nodes. In extreme cases, the tree will linearize, which defends against worst-case behaviors observed in some other data structures.


  1. ^ Selçuk Candan, K.; Luisa Sapino, Maria (31 May 2010). Cambridge University Press, ed. Data Management for Multimedia Retrieval.
  2. ^ Berchtold, Stefan; Keim, Daniel A.; Kriegel, Hans-Peter (1996). "The X-tree: An Index Structure for High-Dimensional Data". Proceedings of the 22nd VLDB Conference. Mumbai, India: 28–39.