Natural Language Processing Lecture 6 Augmented Transition Networks

Natural Language Processing Lecture 6 Augmented Transition Networks Reading: James Allen NLU (Chapter 4) 1

Augmented Transition Networks • An augmented transition network (ATN) is a recursive transition network that can perform tests and take actions during arc transitions. • An ATN uses a set of registers to store information. • A set of actions is defined for each arc, and the actions can look at and modify the registers. • An arc may have a test associated with it. The arc is traversed (and its action is taken) only if the test succeeds. • When a lexical arc is traversed, it is put in a special variable (*) that keeps track of the current word. 2

An ATN for NP 3

An ATN for S 4

1 the 2 dog 3 saw 4 Jack 5 5

An ATN Grammar for Simple Declarative Statements 6

The NP Network 7

The PP Network 8

Definite Clause Grammars 9

S(np(art(the), n(dog)), vp(v(cried))) 10

Definite Clause Grammars • An convenient abbreviated format for writing grammar rules for logic-based parsing systems • Rules can then automatically be compiled into a full database of PROLOG clauses • Omit technical arguments that can automatically be inserted by the system: – word positions and constituent spans – explicit predicates for the lexicon entries • Resulting grammar format looks something like: S(s(Np, Vp), FS) -> NP(Np, FS), VP(Vp, FS) NP(np(Art, Noun), FS) -> ART(Art, FS), N(Noun, FS) VP(vp(Verb), FS) -> V(Verb, FS) 11

A declarative clause grammar 12

Register Presetting Parameter Passing • vp: inf Mary wants to have a party. • _np_vp: inf Mary wants John to have a party. Register VFORM of VP Graph should be preset to inf 13