Anand Rajaraman Jeffrey D. Ullman Querying Websites Using Compact Skeletons. 2001 conf/pods/2001 PODS db/conf/pods/pods2001.html#RajaramanU01 http://doi.acm.org/10.1145/375551.375556 http://www.acm.org/sigs/sigmod/pods/proc01/online/p86.pdf