An enclosed sliding door assembly for simply and efficiently sealing a doorway is disclosed. Summaries of video, audio andor audiovisual data may be provided without any need of knowledge about the true identity of the objects that are present in the data. An approximation is carried out in two directions perpendicular to each other within the modulated data bands to derive unregistered modulated data positioned between the modulated data, thereby modulating the source data. The method then uses a communications protocol between the client and server which allows the client to request one or more of the stored unpaired messages.