Peter Buneman Mary F. Fernandez Dan Suciu UnQL: A Query Language and Algebra for Semistructured Data Based on Structural Recursion. 76-110 2000 9 VLDB J. 1 http://link.springer.de/link/service/journals/00778/bibs/0009001/00090076.htm db/journals/vldb/vldb9.html#BunemanFS00