In order to make database systems interoperate with systems beyond traditional application areas a new paradigm called “exporting database functionality” as a radical departure from traditional thinking has been proposed in research and development. Traditionally, all data are loaded into and owned by the database, whereas according to the new paradigm data may reside outside the database in external repositories or archives. Nevertheless, database functionality, such as query processing and indexing, is provided exploiting interoperability of the DBMS with the external repositories. Obviously, there is an overhead involved having the DBMS interoperate with external repositories instead of a priori loading all data into the DBMS. In this paper we discuss alternatives for interoperability at different levels of abstraction, and we report on evaluations performed using the Concert prototype system making these cost factors explicit.