“…Federated databases offer information integration on demand in dynamic environments, where data warehousing approaches are not feasible (Sheth & Larson, 1990;Geer, 2003). In modern relational database management systems, even non-relational sources can be included in a data federation via "wrappers" so that they can be queried as if they are part of a single large database (Somani, Choy, & Kleewein, 2002;Thiran, Hainaut, Houben, & Benslimane, 2006). Wrappers are mechanisms by which the federated server interacts with non-relational data sources by performing operations such as connecting to a data source and retrieving data from it iteratively.…”