According to one embodiment, a pattern learning system includes a pattern learning tool that receives event messages in a sequential manner from multiple sensors and forms multiple sub-sequences that each includes a trigger event message, a consequence event message, and one or more intermediary event messages. The pattern learning tool then generates multiple graphs that each represents a sub-sequence of the plurality of event messages. The pattern learning tool then combines the graphs into a combined graph according to a type of each event message, and determines a causal sequence from the combined graph according to a heaviest weighted directed path from the trigger event message to the consequence event message.