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CV: Werner Nutt is professor at the Faculty of Computer Science at the University of Bozen since 2005. Prior to this, he was reader at Heriot-Watt University, Edinburgh (2000-2005), visiting professor at the Hebrew University of Jerusalem, and research scientist at the German Research Center for Artificial Intelligence (DFKI) in Saarbruecken (1992-2000). His research interests are in knowledge representation and databases. Abstract: Models of incomplete information have been studied intensively for a long time. More recently researchers have proposed probabilistic data models as an extension, both for relational and tree-structured data, and have investigated the evaluation of non-aggregate queries in these settings. Aggregate queries, however, although of eminent importance in most applications, have received little attention. We will analyse the evaluation of aggregate queries for various probabilistic models of XML. We first give a semantics to queries in this context and define key computational problems. Then we present algorithms and investigate the complexity of the computational problems for several classes of XPath-like queries. Finally, we show how the techniques developed in this framework can be applied to other areas like data streams and data integration. |