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Natural Language Processing

Lecture 6

Augmented Transition Networks

Reading: James Allen NLU (Chapter 4)

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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.

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An ATN for NP

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An ATN for S

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1 the 2 dog 3 saw 4 Jack 5

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An ATN Grammar for Simple Declarative Statements

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The NP Network

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The PP Network

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Definite Clause Grammars

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

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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)

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A declarative clause grammar

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Register Presetting

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