In the preceding chapter we consider trees in which the relative positions of the nodes in the tree are unconstrained. In other words, a given item may appear anywhere in the tree. Clearly, this allows us complete flexibility in the kind of tree that we may construct. And depending on the application, this may be precisely what we need. However, if we lose track of an item, in order to find it again it may be necessary to do a complete traversal of the tree (in the worst case).
In this chapter we consider trees that are designed to support efficient search operations. In order to make it easier to search, we constrain the relative positions of the items in the tree. In addition, we show that by constraining the shape of the tree as well as the relative positions of the items in the tree, search operations can be made even more efficient.