Pablo Barceló, Leonid Libkin, Antonella Poggi, Cristina Sirangelo. XML with Incomplete Information: Models, Properties and Query Answering. In Jan Paredaens and Jianwen Su (ed.), Proc. 28th ACM SIGMOD-SIGACT-SIGART Symposium on Principles of Database Systems (PODS), pp. 237-246, Jun 2009. Providence, Rhode Island. ACM Press, New York, NY, USA. ACM International Conference Proceeding Series. ISBN 978-1-60558-553-6.