LING 581: Advanced Computational Linguistics

Lecture NotesMarch 23rd

Administrivia

• Welcome back!• Task 3 is due

Homework Task

Treebank• There are 180487 VPs in the

Wall Street Journal section• Q: what kinds of verb

frames are attested?EVCA Project• Pick verbs that exist in EVCA

(evca93.index) and also in the PTB

• Produce a report that compares EVCA with what is present in the corpus

Minimalist Syntax

From stochastic parsing to the (near) latest in syntax• Paper:

– Derivation by Phase (DbP) (Chomsky) – (manuscript 1999, published 2001)

• 4 files on usb drive– Reading Homework over Spring Break– dpb.pdf (the unlocked published version)

you may find the following notes very useful– JU_DbP_1.pdf (DbyP with inline notes from Juan Uriagereka)– JU_DbP_2.pdf (part 2)– Yoon_DbP.pdf (notes from James Yoon, UIUC)

Software

• Code– GUI: (Tcl/Tk side) treeserver.tcl– GUI: (Prolog side) prolog_client.pl– Grammar: (GUI version) grammar8.pl

• What you need– Tcl/Tk wish

interpreter– Prolog SWI

Prolog– Command line (some) shell

Processes

• Process #1run treeserver.tcl

under wish interpreter

– example:bash-3.2$ wish treeserver.tclConnection from 127.0.0.1channel closed

• Process #2run SWI-Prolog

– example:bash-3.2$ swiplWelcome to SWI-Prolog (Multi-threaded, 64 bits, Version

5.8.3)

?- [prolog_client, grammar8].% library(error) compiled into error 0.00 sec, 17,480 bytes% library(lists) compiled into lists 0.01 sec, 39,256 bytes% library(shlib) compiled into shlib 0.01 sec, 59,552 bytes% library(unix) compiled into unix 0.01 sec, 65,968 bytes% prolog_client compiled 0.01 sec, 134,368 bytes% grammar8 compiled 0.00 sec, 46,816 bytestrue.

chatter: uses sockets to communicate with Prolog side

Example 1

• John likes Mary• Run in SWI Prolog window?- parse([john,like,mary]).Probe [v*] agrees with goal

[n mary]Probe [t] agrees with goal

[n john][c[c][t[n john][t[t][v[n john]

[v[v*][V[V like][n mary]]]]]]]

true ;false.

Click to see derivation steps

Tree display zoom slider

Agree(P,G) computationsdisplayedterminal parse output: same

as last step of GUI output

Current Limitations• John likes Mary• Run in SWI Prolog window?- parse([john,like,mary]).Probe [v*] agrees with goal

[n mary]Probe [t] agrees with goal

[n john][c[c][t[n john][t[t][v[n

john][v[v*][V[V like][n mary]]]]]]]

true ;false.

Implementation limitations:1. No Spell-Out implemented (just

narrow syntax)T + v* f(phi,3-sg-f)+ V(like) = likes

2. No head movement/affix-hopping implemented (part of Spell-Out)input: awarded -> [ed,award]

3. No undo of displacement implemented(displacement is computed from base position)input:[be,ed,award,several,prizes]Several prizes are awarded

Note: not inflected

Spell-Out: implementation of simple inflectional morphology would be straightforwardParsing from final landing sites would require an additional computational mechanism

Interacting with the Grammar• parse(List).

– Prolog List = input sentence1. Opens a socket connection to

display server2. Calls the definite clause grammar

(DCG) rule for a clause: c(Parse,List,[]).

3. Closes socket connection

• resetDisplay.1. Opens a socket connection to

display server2. Clears the display history for a

derivation3. Closes socket connection

• Components of parse(List) can be called separately– open_connection.– close_connection.– X(Parse,List,[]).

• X = grammar rule name

– useful when other DCG rules need to be called directly

• Implementation (prolog_client.pl)

parse(List) :-open_connection,c(Parse,List,[]),format('~p~n',[Parse]),close_connection.

use after each derivation

Four Examples

Example 1• There are likely to be awarded several

prizes• (note input lexme order)?-

parse([be,likely,there,be,ed,award,several,prizes]).

Probe [a!case ed] agrees with goal [n!case several prizes]

Probe [tdef] agrees with goal [n!case several prizes]

Probe [t!phi] agrees with goal [n!phi there]

Probe [t] agrees with goal [n several prizes]

[c[c][t[n there][t[t][v[v be][a[a likely][t[n there][t[tdef][v[v be][a[a ed][V[V award][n several prizes]]]]]]]]]]]

true ;false.

Example 2• Several prizes are likely to be awarded• (note input lexeme order)?- resetDisplay.true.

?- parse([be,likely,be,ed,award,several,prizes]).

Probe [a!case ed] agrees with goal [n!case several prizes]

Probe [tdef] agrees with goal [n!case several prizes]

Probe [t] agrees with goal [n several prizes][c[c][t[n several prizes][t[t][v[v be][a[a

likely][t[n several prizes][t[tdef][v[v be][a[a ed][V[V award][n several prizes]]]]]]]]]]]

true ;false.

Example 3• we expect there to be awarded several prizes

(note input lexeme order)

?- parse([we,expect,there,be,ed,award,several,prizes]).

Probe [a!case ed] agrees with goal [n!case several prizes]

Probe [tdef] agrees with goal [n!case several prizes]

Probe [v*!phi] agrees with goal [n!phi there]Probe [v*] agrees with goal [n several prizes]Probe [t] agrees with goal [n we][c[c][t[n we][t[t][v[n we][v[v*][V[V expect]

[t[n there][t[tdef][v[v be][a[a ed][V[V award][n several prizes]]]]]]]]]]]]

true ;false.

Example 4• we expect several prizes to be awarded

(note input lexeme order)

?- parse([we,expect,be,ed,award,several,prizes]).

Probe [a!case ed] agrees with goal [n!case several prizes]

Probe [tdef] agrees with goal [n!case several prizes]

Probe [v*] agrees with goal [n several prizes]

Probe [t] agrees with goal [n we][c[c][t[n we][t[t][v[n we][v[v*][V[V expect]

[t[n several prizes][t[tdef][v[v be][a[a ed][V[V award][n several prizes]]]]]]]]]]]]

true ;false.

Basic Computation• start with lexical array of syntactic

objects: {α,..,ω}• Merge “an indispensible operation of a

recursive system”• (external)

– two syntactic objects (SOs): α, β– create merged SO: {α, β}– label({α, β})=label(α) or label(β)

• (internal), implements Displacement– SOs: α and γ, γ properly contained in α – create SO: {α, γ}– label({α, γ})=label(α)

• Agree– active probe SO: α (active =

uninterpretable features), goal SO: β– match and delete uninterpretable features

of probe and goal• Convergent derivation: uninterpretable

features must be eliminated

copy

v*: φ, accN: φ, Case

Basic Implementation (1)Definite clause grammar (DCG) (simplified)

V([V V N]) --> V(V), n(N).

V([V Verb]) --> [Verb].

features (V) features (N)– phonetic matrix: f(pmatrix,like) f(pmatrix,john)

– (takes an) argument: f(arg,+) f(arg,+)

– uninterpretable Case: f(case,_)

% (big V) verb classesbV(n('V',[],[V,N])) --> bV0(V), n0(N), {theta(V),theta(N)} report 'theta merge V & N'.bV0(n('V',[f(pmatrix,Verb),f(arg,+)],[])) --> [Verb], {transitive(Verb)}.bV0(n('V',[f(pmatrix,Verb),f(arg,+)],[])) --> [Verb], {unaccusative(Verb)}.bV0(n('V',[f(pmatrix,Verb)],[])) --> [Verb], {unergative(Verb)}.

transitive(like). transitive(expect).unergative(run). unaccusative(arrive).

n0(n(n,[f(pmatrix,BNoun)|Fs],[])) --> [BNoun], {bareNoun(BNoun,Fs)}.bareNoun(john,[f(phi,3-sg-m),f(case,_),f(arg,+)]).

variable

Basic Implementation (2)

Definite clause grammar (DCG) (simplified)v([v N v]) --> n(N), v(v).

v([v v V]) --> v(v), V(V).

v([v*]) --> [].

– features (v*)• uninterpretable φ-features: f(phi,_-_-_)

• can value accusative Case: f(case,acc)

% v*/vPv(n(v,[],[N,V])) --> n0(N), {theta(N)}, v1(V) report 'theta merge N & v'.v1(n(v,[],[V,BV])) --> v0(V), bV(BV), {goals(BV,Goals),agree(V,Goals)} report 'merge v & V'.v0(n('v*',[f(phi,_-_-_),f(case,acc)],[])) --> [].

triggers Agree

f(phi,_-_-_)f(case,acc)

f(phi,3-sg-f)f(case,_)

Basic Implementation (2)

f(phi,_-_-_)f(case,acc)

f(phi,3-sg-f)f(case,_)

• Agree(v*,N)

Operation: unification (Robinson, 1965)(match and instantiate unvalued features)Probe Goalf(phi,_-_-_) f(phi,3-sg-f)f(case,acc) f(case,_)

Uninterpretable/unvalued features (represented by variables) are eliminated

Basic Implementation (3)

Definite clause grammar (DCG)T([T N v]) --> n(N), v(v).

T([T N v]) --> v(v), {N a goal}

T([T]) --> [].

– features (φ-complete T)• uninterpretable φ-features: f(phi,_-_-_)

• can value nominative Case: f(case,nom)

• EPP

t(n(t,[],[N,T])) --> n0(N), {nonarg(N)}, t1(T,_) report 'merge expl & T'. % EPP: (1) merget(n(t,[],[Goal,T])) --> t1(T,Goal) report 'move to spec-T’. % EPP: (2) move with maximize matching

t1(n(t,[],[T,V]),G) --> t0(T), v(V), {goals(V,Goals),agree(T,Goals), Goals = [G|_]} report 'merge T & v’.t0(n(t,[f(phi,_-_-_),f(case,nom)],[])) --> [].

triggers Agree

defective Tφ-incompletee.g. infinitivals

╳

Putting it all together (1)

Putting it all together (2)

Putting it all together (3)

Putting it all together (4)

Putting it all together (5)

(EPP requirement)

Putting it all together (6)Operation: Spell-Out (not currently implemented)“John likes Mary”only one copy of John is pronouncedbundleT + v* f(phi,3-sg-f)+ V (like) = likes

A Worked Example

Consider the derivation of• several prizes are likely to be awarded (= 4(b)(ii))

awarded = award + -ed (adjectival participle)

?- parse([be,likely,be,ed,award,several,prizes]).Probe [a!case ed] agrees with goal [n!case several prizes]Probe [tdef] agrees with goal [n!case several prizes]Probe [t] agrees with goal [n several prizes][c[c][t[n several prizes][t[t][v[v be][a[a likely][t[n several prizes][t[tdef][v[v be][a[a ed][V[V award][n several prizes]]]]]]]]]]]

ϕ-incomplete: uninterpretable Number and Gender onlyuninterpretable Casemorphologically unrealized in English (cf. Icelandic)

-ed

Agree(a,N)-ed: φ, CaseN: φ, Case

A Worked Example

A Worked Example

Agree(a,N)-ed: φ, CaseN: φ, Case

Notation: !case means feature is unvalued

A Worked Example

Agree(Tdef,N)Tdef: φN: φ, Case

A Worked Example

(several prizes raises to subject position of embedded infinitival)

A Worked Example

Agree(T,N)T: φ, NominativeN: φ, Case

Case for –ed also valuedbecause of earlier unification stepAgree(a,N)-ed: φ, CaseN: φ, Case

Matrix T

Unification presents an possible advantage: computation is more local

Probing with multiple goals

(Chomsky 2001)compare with…

A Worked Example

Spell-OutSeveral prizes are likely to be awarded

Another Example

?- parse([be,likely,there,be,ed,award,several,prizes]).Probe [a!case ed] agrees with goal [n!case several prizes]Probe [tdef] agrees with goal [n!case several prizes]Probe [t!phi] agrees with goal [n!phi there]Probe [t] agrees with goal [n several prizes][c[c][t[n there][t[t][v[v be][a[a likely][t[n there][t[tdef][v[v be]

[a[a ed][V[V award][n several prizes]]]]]]]]]]]

Consider also the derivation of• There are likely to be awarded several prizes(= 4(b)(i))

pleonastic there: φ-incomplete (Person only)

Agree(a,N)-ed: φ, CaseN: φ, Case

Agree(T,N)T: φN: φ

Another Example

Agree(a,N)-ed: φ, CaseN: φ, Case

Examples

(Chomsky 2001)

• Examples (ECM):– (i) we expect there to be awarded several prizes– (ii) we expect several prizes to be awarded

Example: we expect several prizes to be awarded

Prior Unification: locality advantage

Case

Example: we expect several prizes to be awarded

Spell-OutWe expect several prizes to be awarded