Yongqiao Xiao Jenq-Foung Yao G. Yang Discovering Frequent Embedded Subtree Patterns from Large Databases of Unordered Labeled Trees. 70-92 2005 1 IJDWM 2 http://www.igi-pub.com/articles/details.asp?ID=4824 db/journals/jdwm/ijdwm1.html#XiaoYY05