1. A method for improving XML query evaluation, comprising: combining path indices and ancestor information to replace at least one physical index cursor with at least one virtual cursor for processing joins; given an element position p of a child query node, retrieving information describing ancestor positions of element position p and levels at which relevant ancestors appear; and finding the first ancestor position pa for which these conditions hold: (1) ancestor position pa>element position pcur, where pcur is the current element position of the virtual cursor, and (2) ancestor position pa is relevant to the virtual cursor, because ancestor position pa has an appropriate tag or text value; wherein the number of postings handled for a join is decreased by modifying the virtual cursors to ignore all postings with non-qualifying path IDs; and wherein movement of the virtual cursors never triggers index I/O operations as the need to scan postings for all internal, non-leaf posting lists is deliberately avoided.
1. A method for improving XML query evaluation, comprising: combining path indices and ancestor information to replace at least one physical index cursor with at least one virtual cursor for processing joins; given an element position p of a child query node, retrieving information describing ancestor positions of element position p and levels at which relevant ancestors appear; and finding the first ancestor position pa for which these conditions hold: (1) ancestor position pa>element position pcur, where pcur is the current element position of the virtual cursor, and (2) ancestor position pa is relevant to the virtual cursor, because ancestor position pa has an appropriate tag or text value; wherein the number of postings handled for a join is decreased by modifying the virtual cursors to ignore all postings with non-qualifying path IDs; and wherein movement of the virtual cursors never triggers index I/O operations as the need to scan postings for all internal, non-leaf posting lists is deliberately avoided. 2. The method of claim 1 further comprising: performing the retrieving once for a given path ID and token; and saving the retrieved information for re-use for future queries.