The consistency issues have been well studied in term of methodologies and technologies for the most popular interaction paradigm, namely the client-server. In the agent's world such a paradigm is used as much as another one, the notification-observation, in which an active system notifies its status changes to registered observer agents. In the client-server paradigm, when a client invokes a read operation of the system, the latter is always able to reply with a consistent status. Also in the notification-observation paradigm, the perception of consistent status changes of the observed system is a requirement, in order to take decision correctly. But the above-mentioned instruments used for the client-server scenario, are not suited for the notificationobservation paradigm. In this paper we highlight the problem and propose an abstraction called observation interface, as an architecture allowing observer agents to perceive consistent status changes of an active system.