Virtual cursors for XML joins

Structural joins are a fundamental operation in XML query processing and a large body of work has focused on index-based algorithms for executing them. In this paper, we describe how two well-known index features - path indices and ancestor information - can be combined in a novel way to replace one or more of the physical index cursors in a structural join with virtual cursors. The position of a virtual cursor is derived from the path and ancestor information of a physical cursor. Implementation results are provided to show that, by eliminating index I/O, virtual cursors can improve the performance of structural joins by an order of magnitude or more. Copyright 2004 ACM.