A dynamic construction algorithm for the Compact Patricia trie using the hierarchical structure

We need to access objective information efficiently and arbitrary strings in the text at high speed. In several key retrieval strategies, we often use the binary trie for supporting fast access method in order. Especially, the Patricia trie (Pat tree) is famous as the fastest access method in binary tries, because it has the shallowest tree structure. However, the Pat tree requires many good physician storage spaces in memory, if key set registered is large. Thereby, an expense problem happens when storing this trie to the main storage unit. We already proposed a method that use compact bit stream and compress a Pat tree to solve this problem. This is called Compact Patricia trie (CPat tree). This CPat tree needs capacity of only a very few memory device. However, if a size of key set increases, the time expense that search, update key increases gradually. This paper proposes a new structure of the CPat tree to avoid that it takes much time in search and update about much key set, and a method to construct a new CPat tree dynamically and efficiently. This method divides a CPat tree consisting of bit string to fixed depth. In addition, it compose been divided CPAT tree hierarchically. A construction algorithm that proves this update time requires alteration of only one tree among whole trees that is divided. From experimental result that use 120,000 English substantives and 70,000 Japanese substantives, we prove an update time that is faster more than 40 times than the traditional method. Moreover, a space efficiency of memory increases about 35% only than the traditional method. (C) 2001 Published by Elsevier Science Ltd.