An alerting system is provided that includes a network of transformation nodes, and a state change processors. The transformation nodes include input transformation nodes, output transformation nodes, and intermediate nodes that connect the input and output transformation nodes. Each input transformation node can receive an events stream, and is coupled to one of the output transformation nodes by one or more intermediate transformation nodes. Each transformation node (except the input transformation nodes) can receive state updates from those transformation nodes that it subscribes to. Each output transformation node can generate a check result when stored state information for each of the transformation nodes that the output transformation node subscribes to collectively indicates that the check result should be generated. Each output transformation node is coupled to one of the state change processors that can determine whether the check results should trigger an action, and if so, can then perform an action.