A Model of Alerting Services in Wide Area Networks Annika Hinze Institute of Computer Science Freie Universit¨ at Berlin, Germany hinze@inf.fu-berlin.de 1 Introduction Since the number of scientific publications doubles every 10 - 15 years [8], there is strong need for the use of alerting services. An alerting service keeps the users informed about new documents and events they are interested in. An alerting service can be build on top of a low-level event notification service as used for distributed control mechanisms or device monitoring. Conceivable techniques are CORBA Event and Notification Service, Java Distributed Events and Messaging Service and others. The underlying model of these services differs from the conditions found in applications suitable for wide area networks, such as digital libraries. Here we provide a model for alerting services that considers the special constraints of this application area. The remainder of this paper is structured as follows: Section 2 introduces the main concepts of data dissemination services, Section 3 provides an overview of related research topics and existing notification services. Section 4 outlines the new model of alerting services. In Section 5, we conclude with the direction for future work. 2 Data Dissemination The application domain we consider covers such applications as stock tickers, common weather report channels, notification about new items in digital libraries or traveler information systems. The range of services for data dissemination reaches from awareness services (to keep replicated data consistent) to event-based infrastructure for distributed control. Alerting services connect providers of information and interested clients, they inform the clients about the occurrence of an event on provider side. Clients define their interest in personal profiles. The infor- mation about the events is filtered according to these profiles and notifications are send to the interested users. Figure 2 depicts the data-flow in an high-level architecture of an alerting service. (Keep in mind that the data-flow is independent from the delivery mode.) The tasks of an alerting service subdivide Object of Interest Alerting Service Interested Party Profile Notification Event Data publish notify subscribe Figure 1: Data-flow in an alerting service into the following steps: First the observable event classes are to be determined and offered to the clients. Then the clients profiles have to be defined and stored. The occurring events have to be observed. Before creating notifications the events have to be integrated in order to detect event patterns. After duplicate recognition the event messages have to be stored in order to enable efficient notification. According to a