A method and an arrangement for providing resource data for at least one resource to a watching client. A subscription request for resource data regarding a resource sent from a watching client is received (700) by a notification server, the subscription request comprising a reference to notification rule being pre-configured in a database for the watching client. The delivery of notifications to the watching client is controlled (710) based on the reference. Supplementing the subscription requests with a reference to pre-configured notification rules regarding the observed resource(s) instead of the actual notification rules, reduces the amount of information being transferred with plural subscription requests for a watching client.