Compressed tries

Abstract

This paper presents a new data structure, called a compressed trie or C-trie, to be used in information retrieval systems. It has the same underlying m-ary tree structure as a trie, where m is a parameter of the trie, but whereas the fields of the nodes in a trie have to be large enough to hold a key or at least a pointer, the fields in a C-trie are only one bit long. In the analysis part of the paper it will be shown that for a collection of n keys the retrieval time, measured in terms of bit inspections of one key, is of the order log m n and the storage requirement of the order n·(m + log 2 n) bits. This improvement in storage requirements and retrieval time is achieved at the cost of decreasing the flexibility of the structure, and therefore updating costs are increased. First the C-trie is analyzed as a data structure, and then several methods of its use for relatively static databases are discussed.