IMPROVED PARTIAL-MATCH SEARCH ALGORITHMS FOR BD-TREES

Partial-match search queries form an important class of queries posed to a database system. Several storage structures have been proposed to answer these queries efficiently. The BD tree is an example of such a storage structure. A partial-match search algorithm, called A(ORIG), is given in Ref. 5. This paper presents three algorithms - A(LOCAL), A(COMP) and A(GLOBAL) - that represent three levels of improvement to A(ORIG). Each one yields successively more benefit at the cost of more complexity. All the improvements centre on avoiding the exploration of unnecessary OUT branches. It is shown that A(GLOBAL) is the best partial-match search algorithm in the sense that no other algorithm searches fewer internal and external nodes. The worst-case complexity of performing a partial-match search in BD trees using A(GLOBAL) is shown to be the same as that for the k-d trees.