R树的特性：
Let M be the maximum number of entries that
will fit in one node and let m≤M/2 be a parameter specifying the minimum number of entries in a
node
假设M是适合于一个结点的最大条目数，m≤M/2是特定最小条目数
(1) Every leaf node contains between m and M index records unless it is the root
每一个叶子结点都包含m至M个索引记录，除了根结点
(2)For each index record (I, tuple-identifier) in a leaf node, I is the smallest rectangle that
spatially contains the n-dimensional data object represented by the indicated
tuple.
对于叶子结点的每一条索引记录(I, tuple-identifier)，I是数组所表示的n维数据对象的最小外接矩形
(3) Every non-leaf node has between m and M children unless it is the root.
每一个非叶子结点都有m至M个孩子结点，除了根结点
(4) For each entry (I, child-pointer) in a non-leaf node, I is the smallest rectangle that spatially contams the rectangles
in the child node.
每一个非叶子结点的条目(I, child-pointer)，I是包含所有孩子结点外接矩形的最小矩形
(5) The root node has at least two children
unless it is a leaf
根结点至少有两个孩子结点，除非它是叶子结点
(6) All leaves appear on the same level
所有叶子结点都在同一层
R+树的特性：
(1) For each entry (p, RECT) in an
intermediate node, the subtree rooted at the node pointed to by p contains a
rectangle R if and only if R is covered by RECT. The only exception is when R
is a rectangle at a leaf node; in that case R must just overlap with RECT.
对于中间结点的（p, RECT），当且仅当R被RECT覆盖（covered）时，p指向的结点的子树才包含R；
(2) For any two entries (p1, RECT1) and (p2,
RECT2) of an intermediate node, the overlap between RECT1 and RECT2 is zero.
对于某个中间结点的任意两个条目（entry）（p1,RECT1）和（p2,RECT）都无重叠；
(3) The root has at least two children
unless it is a leaf.
根结点至少有两个孩子结点，除了叶子结点；
(4) All leaves are at the same level.
所有叶子结点都在同一层。
各位网友都帮看看，翻译的准确不，特别是那个entry，不知道翻译成什么比较贴切！
