On the Efficiency of a New Method of Dictionary Construction

Programs for constructing dictionaries of texts, with computers, have sometimes been adaptat ions of methods suitable for manual construction with card indexes. With all card index methods it is customary to keep the different words collected in alphabetical order, for the structure of a card index lends itself to such a process: all tha t is necessary to insert ~ new word into the index between two existing ones is to make out a new card and to put it in the correct place. However, the insertion of a new word in the store of a computer where the words are kept in alphabetical order is a t ime-consuming process, for all the words below the one which is inserted have to be "moved down" by one place. If, however, a computer method is used where the words are not stored in alphabetical order but in the order in which they occur, the position is even worse, for although the shifting of words is eliminated, the dict ionary search which is necessary for each word in the text, to establish whether it is a new word or not, must involve all the words collected so far, and not: iust a small number of them, as would be the ease if the words were in alphabetical order, and a logarithmic search (Booth, 1955) could be used. The method of construction described in this paper overcomes both these problems. I t is no t an adaptat ion of a manual method, but is designed specifically for computers. The method is based on a tree structure, which is discussed below.