Retrieving XML Data from Heterogeneous Sources through Vague Querying

We propose a framework for querying heterogeneous XML data sources. The framework ensures high autonomy to participating sources as it does not rely on a global schema or on semantic mappings between schemas. The basic intuition is that of extending traditional approaches for approximate query evaluation, by providing techniques for combining partial answers coming from different sources, possibly on the basis of limited knowledge about the local schemas (i.e., key constraints). We define a query language and its associated semantics, that allows us to collect as much information as possible from several heterogeneous XML sources. We provide algorithms for query evaluation and characterize the complexity of the query language. Finally, we validate the approach in a medical application scenario.