Multikey index structures for type hierarchies are a recently discussed alternative to traditional B/sup +/-tree indexing schemes. We describe an efficient implementation of this alternative called the multikey type index (MT-index). A prerequisite for our approach is an optimal linearization of the type hierarchy that allows us to map queries in object type hierarchies to minimal-volume range queries in multi-attribute search structures. This provides access to an already-existing large and versatile tool-box. The outline of an index implementation by means of a multi-attribute search structure (e.g. the hB-tree or any other structure with comparable performance) is followed by an analytical performance evaluation. Selected performance figures are compared to previous approaches, in particular to the H-tree and the class hierarchy tree. The comparison results allow for practically relevant conclusions with respect to index selection based on query profiles.

Disk input/output (I/O) efficient query execution is an important topic with respect to DBMS performance. In this context, we elaborate on the construction of disk access plans for sort order queries in balanced and nested grid files. The key idea is to use the order information contained in the directory of the multiattribute search structure. The presented algorithms are shown to yield a significant decrease in the number of disk I/O operations by appropriate use of the order information. Two algorithms for the construction of appropriate disk access plans are proposed, namely a greedy approach and a heuristic divide-and-conquer approach. Both approaches yield considerable I/O savings compared to straightforward query processing without consideration of any directory order information. The former performs well for small buffer page allocations, i.e., for a small number of buffer pages relative to the number of data buckets processed in the query. The latter is superior to the greedy algorithm with respect to the total number of I/O operations and with respect to the overall maximum of buffer pages needed to achieve the minimal number of disk I/O operations. Both approaches rely on a binary trie as a temporary data structure. This trie is used as an explicit representation of the order information. The storage consumption of the temporary data structure is shown to be negligible in realistic cases, Even for pathological cases with respect to degenerated balanced and nested grid files, reasonable upper bounds can be given.>