1. A method of controlling distribution of content-related metadata from different content-related sources ( 101 - 1 to 101 - n ), said method comprising: a) receiving said metadata at an intermediate location between said content-related sources ( 101 - 1 to 101 - n ) and a recommender engine ( 107 ); b) processing the received metadata at said intermediate location to transform a received format ( 1021 , 1022 ) of said received metadata into a predetermined common format ( 1026 ) used by said recommender engine ( 107 ); c) forwarding the processed metadata to a metadata base ( 103 ); and d) checking whether said received format ( 1021 , 1022 ) of said extracted metadata is a known format, discarding said extracted metadata and sending a corresponding information to a source of said received format if said received format ( 1021 , 1022 ) is an unknown format.