Arabic Syntactic Trees

Zdeněk ŽabokrtskýOtakar Smrž

Center for Computational LinguisticsFaculty of Mathematics and PhysicsCharles University in Prague

from Constituency to Dependency

April 15, 2003 Arabic Syntactic Trees: from Constituency to Dependency 2

Motivation & Background Linguistic Data Consortium Arabic Treebank

Constituent-syntax bracketing ~100k words published Modification from English to Arabic

Prague Arabic Dependency Treebank Dependency approach to syntax ~50k words in

progress Pre-step to tectogrammatical description

Motivation: co-operation and resource exchange Our goal: transform the data from one annotation

scheme to the other

April 15, 2003 Arabic Syntactic Trees: from Constituency to Dependency 3

Constituency X Dependency Non-terminal nodes

+ Text tokens Constituent labeling

on non-terminals Slots and traces

Linguistic Data Consortium, University of Pennsylvania

Sentence root node + Text tokens

Analytical function for every tree node

Government and roles

CCL & IFAL & ICL, Charles University in Prague

April 15, 2003 Arabic Syntactic Trees: from Constituency to Dependency 4

Model Arabic Phrase I Trace of the antecedent

subject Compound function of

the head of the clause – outer and inner perspectives

Free word-order compliant

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Outline of the Transformation

1. Build temporary dependency tree Contraction of the input phrase-structure tree Uniquely determined by head selection function Implementation: simple recursive procedure

2. Create analytical tree topology Post-processing (corrections) of the temporary dep.

tree, e.g., substituting traces with trace coindexed fillers

Re-arrangement of special complex constructs

3. Assign analytical functions

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Head Selection Function For each constituent, select the head

constituent among its children Based on (ordered) handcrafted rules Examples:

If there is a node with tag=PREP among the children, then it is the head

If there is a node with phrase_label=VP among the children, then it is the head

... etc ... If nothing was selected by the rules, then the

rightmost child is selected

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Analytical Function Assignment

Based on (ordered) handcrafted rules and lexical lists

Completes the process, does not override previous assignments

Examples: phrase_label=NP-SBJ afun=Sb lemma=wa- afun=Coord pos_tag=CONJ afun=AuxC ... etc ...

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Model Arabic Phrase II Sister-like co-ordination Conjunction of co-ordination

Status constructus

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Model Arabic Phrase III Non-expressed subject (?) Complex modality

constructs Principal discrepancies

between descriptions – both in topology and labeling

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Model Arabic Sentence Wa lam yakun mina ’s-sahli `alay hi

muwāğahatu kāmīrāti ’t-tilfizyūni wa `adasāti ’l-muşawwirīna wa huwa yaş`adu ’l-bāşa.

It was not easy for him to face the television cameras and the lenses of photographers as he was getting on the bus.

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Constituency Annotation

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Dependency Annotation

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Evaluation & Conclusion Implementation still in progress, fine-tuning

needed

10,000 words manually annotated in both styles ~60% of correctly aimed dependencies

2nd Prague Penn Arabic Treebanking Workshop, May 2003 in Prague

Transfer from dependency to constituency?

April 15, 2003 Arabic Syntactic Trees: from Constituency to Dependency 14

Related Work New tool for assignment of analytical functions

Based on machine learning (C5-trained decision trees) Error rate 17% (supposing the topology of the tree is

correct)

First experiments with Arabic dependency parser

Incorporated into the process of annotation of Prague Arabic Dependency Treebank