The updating of data files in the form of doubly chained trees, and the amount of effort required to maintain such trees, are discussed.The paper offers a strategy for overcoming the updating problem, as well as some general methods for quantifying the maintenance effort and for implementing the operations.

It is shown that, owing to certain restrictions placed upon the set of admissible structures, some previous solutions have not characterized trees in which expected search time is minimized. The more general problem is shown to be a special case of a coding problem, which was previously formulated and solved as a linear integer programming problem, and in the special case of equally probable key requests is found to be solvable almost by inspection. Some remarks are given regarding the possibility of realizing a shorter computational procedure than would be expected from an integer programming algorithm, along with a comparison of results from the present method with those of the previous.