In examples, a system adaptively orders a set of regular expressions based on frequencies that respective regular expressions of the set of regular expressions match a set of messages, the adaptive ordering to produce an adaptively ordered set of regular expressions. The system determines, for a first message of the set of messages, whether a plurality of regular expressions of the adaptively ordered set of regular expressions match the first message. The system constructs a bi-directional graph representing the plurality of regular expressions that match the first message, and classifies a second message based on the adaptively ordered set of regular expressions and the bi-directional graph.