1. A method for integrating data in a database management system, said method comprising: grouping data sources and replicas of said data sources that provide analogous data into a common logical domain; writing application queries against said common logical domain; selecting a correct set of replicas of said data sources and a query-execution strategy for combining a content of said correct set of replicas of said data sources in order to answer said application queries according to query-cost-based optimization; selecting a correct set of data sources according to run-time constraints; shielding said application queries from changes to said data sources by dynamically binding said application queries against the correct sets of data sources and replicas of said data sources; and processing said application queries by generating an optimum query result based on said grouping and said shielding.