An application module generates a query that may involve retrieving data from a local data storage source or from an external data storage source. The application module retrieves metadata to form a query tree stored in the local data storage source and uses the query tree to ascertain one or more sub-queries necessary to complete the query and whether the necessary data for each sub-query is stored locally or externally. Based on the location of the data to complete a sub-query, the application module uses the services of an internal query processing layer if external data is involved for the sub-query. The application module uses the services of a query processing layer in the local data storage source if the data is local. Once all the sub-queries associated with the query tree are performed, then the overall query results are returned to the application module.