unification grammar

Unification Grammar

Trying to solve the same problems

Phrase structure rules

Transformational Grammar has PSRs

But it also needs features

And features may move

Or be copied

Transformational Grammars ALSO need MOVEMENT

PSRs, features, and movement

Unification Grammars

No movement

Phrase Structure Rules -- yes

Movement -- no

Just structure-sharing

Structure-sharing MEANS unification

And VERY complicated information IN words!

Attribute-value matrix

Head-driven Phrase Structure Grammar

HPSG

HPSG is the most popular Unification Grammar

Attribute-value matrix (AVM)

AVMs MODEL words

This is a model of a word

Very complex and structured

Words have ATTRIBUTES

For example PHON

PHON is phonological or sound-related information

Nobody cares about PHON

Unless they’re PHONologists!

SYNSEM is an attribute

SYNSEM is the syntactic and semantic information

We DO care about SYNSEM

LOCAL is an attribute

Forget about it for now

CATEGORY or CAT

CAT carries the syntactic features

What kind of word is it?

[She] is a noun

HEAD attribute is noun

Nominative CASE

CONTENT and CONTEXT is the semantic info

[She] is 3rd person

[She] is singular

[She] is feminine

[She] CONTENT

• PER 3rd

• NUM sing• GEND fem

HEAD attribute is verb

[walks][walks]

[walks] has VALENCE attributes

[walks][walks]

VALENCE is also known as SUBCAT

[walks][walks]

VALENCE/SUBCAT who cares?

[walks][walks]

VALENCE sounds more scientific

[walks][walks]

VALENCE means attract or repel

[walks][walks]

[walks] attracts a noun

[walks][walks]

[walks] attracts a subject

[walks][walks]

[walks] specifies information about the subject

[walks][walks]

[walks]

SUBJ<CAT|HEAD noun|CASE nominative CONT [1]|PER 3rd

NUM singGEND –

CONT|walker [1]

CONT of subject matches in CONT of the verb

SUBJ<CAT|HEAD noun|CASE nominative CONT [1]|PER 3rd

NUM singGEND –

CONT|walker [1]

If the verb takes [she] as a subject …

SUBJ<CAT|HEAD noun|CASE nominative CONT [1]|PER 3rd

NUM singGEND –

CONT|walker [1]

CONT [1] matches CONT of [she]

SUBJ<CAT|HEAD noun|CASE nominative CONT [1]|PER 3rd

NUM singGEND –

CONT|walker [1]

If the verb takes [she] as a subject

SUBJ<CAT|HEAD noun|CASE nominative CONT [1]|PER 3rd

NUM singGEND –

CONT|walker [1]

[She] CONTENT

• PER 3rd

• NUM sing• GEND fem

[She] CONTENT

• PER 3rd

• NUM sing• GEND fem

So when [walks] takes [she] …

SUBJ<CAT|HEAD noun|CASE nominative CONT [1]|PER 3rd

NUM singGEND –

CONT|walker [1]

This …

SUBJ<CAT|HEAD noun|CASE nominative CONT [1]|PER 3rd

NUM singGEND –

CONT|walker [1]

… becomes this

SUBJ<CAT|HEAD noun|CASE nominative CONT [1]|PER 3rd

NUM singGEND fem

CONT|walker [1]

[walks] VALENCE features and CONT features

Notice the structure-sharing

Usually marked with a number in a square

Why is it a number in a square?

Why not?

Who cares?

Could be a color

Or a funny shape – it doesn’t matter

The number in the square shows the structure-sharing

It shows the UNIFICATION

That’s it!

STRUCTURE A = [m _ t _ h]STRUCTURE B = [_ a _ c _]

Unify A and BWhat happens?A+B = [match]That’s it!

It looks complicated

STRUCTURE A = [s _ a _ e]STRUCTURE B = [_ h _ r _]

Unify A and BWhat happens?A+B = [share]But it’s basically very simple (and no movement)

Here’s some [walks] info again!

Notice the VALENCE specifications

[Walks] attracts a NP with nominative case

Walks attracts a NP with CONT [3rd,sing]

[she] has CASE nom

[she] has CONT 3rd, sing, fem

No problem

• She walks • That’s a good sentence

• What about this?• Her walks• Is that a good sentence?• No• Why?

Here’s [her]

[walks] attracts a NP[nom]

[her] is CASE acc (accusative)

The CONT of [her] is OK

But it is the wrong syntactic CATEGORY

Unification fails …

… if there is a mismatch

So don’t panic …

[walks][walks]

… when you see these complicated AVMs

[walks][walks]

It takes a bit of time …

[walks][walks]

You have to get used to it

[walks][walks]

But it’s basically very simple

[walks][walks]

And no movement

[walks][walks]

Don’T forget -- VALENCE features

[walks][walks]

VALENCE or SUBCAT

[walks][walks]

[walks] attracts a noun

[walks][walks]