A technique for reducing the number of events that are transmitted by a server to a client/server application programming interface (API). At the server host, each of different event messages is associated with at least one event category in a hierarchy of event categories. Each client host sends a registration request to the server host in order to inform the host server host that the client wants to receive event messages associated with a specified event category. The server host associates the specified event category with each client host and communicates the event messages that are descendants of the specified event category, wherein the event messages may be descendants of more than one specified event category.