R-tree as a height balanced tree and multidimensional index structure, is very suitable for establishment of multidimensional indexes for file metadata. It can return the result of precomputation quickly to improve queries efficiency. RCube采用R树来作为它的索引结构,它是一棵高度平衡的树,是一种多维的索引结构,非常适用于对文件元数据建立多维索引,能够快速的返回预计算结果,提高查询效率。