Fast result enumeration for keyword queries on XML data

In this paper, we focus on efficient construction of tightest matched subtree (TMSubtree) results for keyword queries on XML data based on SLCA semantics, where “matched” means that all nodes in a returned subtree satisfy the constraint that the set of distinct keywords of the subtree rooted at each node is not subsumed by that of any of its sibling node, while “tightest” means that no two subtrees rooted at two sibling nodes can contain the same set of keywords. Assume that d is the depth of a given TMSubtree, m is the number of keywords of a given query Q, we proved that if d ≤ m, a matched subtree result has at most 2m! nodes; otherwise, the size of a matched subtree result is bounded by (d−m+2)m!. Based on this theoretical result, we propose a pipelined algorithm to construct TMSubtree results without rescanning all node labels. Experiments verify the benefits of our algorithm in aiding keyword search over XML data.