Query optimization in Data stream

I am confused about the idea of query optimization in stream of data. As a background, i know that optimization for any query is happen inside the DBMS with using of System catalogs which contain info. about the tables, columns etc., whatever, the optimization or evaluation process happen inside the DBMS.

What about Data stream, where is the optimization process happen ? suppose that we have (A) device that has an application which send query to device (B) that has the whole DBMS with database. if the optimization process (OP) happen in DBMS (in device B), so we don't have any problem for OP, but it's not happen here since there are a lot of researches to overcome optimization issue in data stream !. And if the process happen in device (A), it's not possible ! since there is no DBMS their !!!

Here a paper Rate-Based Query Optimization for Streaming Information Sources that talk about optimization, but there are no enough info. about where the process happen?