A clustering algorithm for hierarchical structures

The problem of determining how to store a hierarchic structure in order to minimize the expected access time to it is examined. A paging environment is assumed. The solution space considered is the set of partitions of the hierarchic structure, each partition being stored in heirarchical order. A very fast algorithm which determines the optimal partition of the tree is described. The algorithm has been used to determine the best partition of an IMS type tree into data set groups as well as to evaluate the cost of different alternatives. Actual measurements against the restructured databases have shown the validity of the model used by this method. The measurements have also shown that selecting the wrong choice of clustering instead of the optimal one may substantially increase the expected access time.