1. A method for processing a database query on a set of data resulting in an access plan, comprising the steps of: (a) calling a data manager by a query manager to access a query-specified data in the set of data, (b) performing a callback to the query manager by the data manager, (c) indicating to the data manager by the query manager, in response to the callback, whether the query-specified data satisfies the filtering criteria, (d) returning the query-specified data by the data manager based on the response from the query manager to the callback.