A version space algorithm for learning extracting rules from tree-structured documents. Resulting hypotheses are called "tag tree patterns". A Mapping from tag tree patterns to statements in the XPath language is defined.
V. Spiliopoulos, A. Valarakos, and G. Vouros. Proceedings of the 5th European Semantic Web Conference, Berlin, Heidelberg, Springer Verlag, (June 2008)