The Complexity of Trie Index Construction

Trle structures are a convenient way of indexing files in which a key consists of a number of attributes Records correspond to leaves in the trle Retrieval proceeds by following a path from the root to a leaf, the choice of edges being determined by attribute values The size of a trle for a file depends on the order in which attributes are tested It is shown that determining minimal size tries IS an NP-complete problem for several variants of tries and that, for tries m which leaf chains are deleted, determining the trie for which average access time is minimal is also an NP-complete problem These results hold even for files in which attribute values are chosen from a binary or ternary alphabet KE] WORDS AND PHRASES reformation retrieval,