A content management system formed from a playback apparatus that requests and plays content, and a content management apparatus that manages duplication and deletion of content. The playback apparatus notifies group information of the playback apparatus to the content management apparatus, acquires...http://www.google.com.au/patents/US7752433?utm_source=gb-gplus-sharePatent US7752433 - Content-duplication management system, apparatus and method, playback apparatus and method, and computer program
