Outline of AMPEL, acting as broker. Four alerts, A–D, belonging to a unique transient candidate are being read from a stream. In a first step, “Tier 0”, the alert stream is filtered based on alert keywords and catalog matching. Alerts B and D are accepted. In a second step, “Tier 3”, the external resources that AMPEL should notify are chosen. In this example, only Alert D warrants an immediate reaction. The final column shows the corresponding database events.