Augmented Transition Networks (ATNs) A mechanism for integrated syntactic and semantic processing. Far more powerful than the pattern-matching techniques used in ELIZA. ATNs continue to be used in serious work in Natural Language Processing. An ATN is a collection of graphs consisting of "nodes" connected with arrows. Parsing proceeds by starting at some "start" node and traversing arrows until a "done" node is reached. The traversal of each arrow generally "consumes" some part of the input, and may additionally perform other actions (such as setting the values of variables -- this power is what makes ATNs "augmented"). ATNs can have arbitrary actions on transitions.