Riemann’s dependency resolution system expresses stateful relationships between events. Dependencies are expressed as Rules; a Rule is a statement about the relationship between a particular event and the current state of the index.

Maps are rules which specify that their keys and values should be present in some event in the index. {} will match any non-empty index. {:service “a” :state “ok”} will match an index which has {:service “a” :state “ok” :metric 123}, and so on.

(all & rules) matches only if all rules match.

(any & rules) matches if any of the rules match.

(localhost & rules) states that all child rules must have the same host as the event of interest.

(depends a & bs) means that if a matches the current event (and only the current event, not the full index), b must match the current event and index.