Cheng Luo Zhewei Jiang Wen-Chi Hou Gultekin Özsoyoglu Progressive Evaluation of XML Queries for Online Aggregation and Progress Indicator. 382-395 2009 DEXA http://dx.doi.org/10.1007/978-3-642-03573-9_33 conf/dexa/2009 db/conf/dexa/dexa2009.html#LuoJHO09