[Object] To provide a network system capable of efficiently carrying out synchronous processing by positively notifying a home network appliance of an update content of a content or metadata.[Solving Means] A subscriber in a home network appliance acquires via a network an update notification message that stores update information of a content or metadata and in which a filter attribute for categorizing the update notification message is set. The appliance includes a service client that updates, by an application corresponding to a specific service, the content or the metadata in a local content/metadata database using the update information within the update notification message. The subscriber manages a correspondence between the service client and the filter attribute and specifies the service client that provides the update information within the update notification message based on the filter attribute set in the update notification message and the correspondence.