27. A method, implemented in a data processing system, for managing and querying a plurality of inter-related data sources, the method comprising: generating a federated schema that describes structures of the plurality of inter-related data sources and inter-relationships of the plurality of inter-related data sources; modifying the federated schema over time as the plurality of inter-related data sources undergo changes, wherein each of the plurality of inter-related data sources has a corresponding schema that describes a corresponding data structure of a corresponding data source; generating a query for the federated schema; and storing the federated schema.
27. A method, implemented in a data processing system, for managing and querying a plurality of inter-related data sources, the method comprising: generating a federated schema that describes structures of the plurality of inter-related data sources and inter-relationships of the plurality of inter-related data sources; modifying the federated schema over time as the plurality of inter-related data sources undergo changes, wherein each of the plurality of inter-related data sources has a corresponding schema that describes a corresponding data structure of a corresponding data source; generating a query for the federated schema; and storing the federated schema. 48. The method of claim 27 wherein the plurality of inter-related data sources of diverse types include at least one XML document data source and one IBM DB2 database.