Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Posting-Version: version B 2.10 5/3/83; site rochester.UUCP Path: utzoo!watmath!clyde!floyd!harpo!seismo!rochester!blenko From: blenko@rochester.UUCP (Tom Blenko) Newsgroups: net.lang Subject: Re: What's an Augmented Transition Network? Message-ID: <5456@rochester.UUCP> Date: Mon, 5-Mar-84 22:54:07 EST Article-I.D.: rocheste.5456 Posted: Mon Mar 5 22:54:07 1984 Date-Received: Tue, 6-Mar-84 07:01:56 EST References: <144@forcm5.UUCP> Organization: U. of Rochester, CS Dept. Lines: 45 Augmented transition networks (ATN's) are an extension of finite state machine models for parsers. They were first applied by Bill Woods and others at BBN for parsing of natural language. A recursive transition networl (RTN) is just like a finite state machine, except that "pushes" of subnetworks are permissible transitions. Thus S: [NP] [VP] ----->SSub----->SPred NP: [Art] [Noun] +------>Det+------->HN | | -----------> VP: [Verb] [NP] -------->Mv+-------+>Vp | | --------> might represent a grammar in which a sentence (S) consists of a noun phrase (NP) followed by a verb phrase (VP). The NP transition succeeds if an optional article (Art) followed by a noun (Noun) can be read from input. Similarly, the VP transition succeeds if a verb is read from input, and an optional noun phrase can be "pushed". Clearly an RTN is no more powerful than a finite state parser, but it is easier to write grammars for! An ATN is an RTN extended to handle (virtually arbitrary) conditionals attached to the transitions. This was intended to capture some of the semantics (some would argue it's all syntax) of the language. For example, a part of a grammar might apply to prepositional phrases for "place where": these would check at the beginning of the phrase to make sure that the preposition was one of {to, from, at}. There is also a capability for storing values in registers on a "push". This is useful for handling relative clauses, for example, in the which the noun modified in the main sentence might be used as either the subject or object of the the relative clause. Tom