Counting relaxed twig matches in a tree. Dongwon Lee and Divesh Srivastava. We consider the problem of accurately estimating the number of approximate XML answers for a given query, and propose an efficient method that (1) accurately computes selectivity estimates for each relaxed XML query, using a natural generalization of the correlated subpath tree (CST) summary structure, and (2) carefully combines these estimates by analyzing the nature of overlap between the different relaxed twig queries.