Two fundamental approaches for database integration exist: the data warehouse approach attempts to physically merge data sets from several source databases, whereas database federations simultaneously query source databases online. In this paper, a database federation approach based on two components is introduced. MARGBench is a system which, among other features, enables the querying of several databases in SQL by translating SQL queries into a source database-specific interface. In this system, SQL queries use the database field labels of the original database, i.e. fields that contain the same kind of information are labelled differently in different databases. In order to solve this problem, a second system, based on ontologies, is currently being developed. This ontology system not only includes information about the semantics of database fields but also contains information about the databases themselves. Thus, it facilitates both database binding and intelligent database querying. The main concepts and ideas of these two systems are explained. By using an imaginary database query, it is demonstrated how the two systems (the ontology system and MARGBench) work together in order to enable the querying of several databases simultaneously.