It is an object of the present invention to relieve the burden on a watcher that uses a presence system to subscribe to the presence information of people and objects. For example, an attribute is a product name, and products A, B, C have the identical attribute value “DVDRecorder.” The server generates aggregate presence information, which includes the presence information of the products A, B, C (corresponds to the providers), and sends a notification of such to a watcher W (corresponds to the notification recipient) of the presence information of the products A, B, C. The watcher W collectively receives the presence information for every product name, and the watcher W is therefore relieved of the burden of classifying the presence information for every product name.