Arabic Syntactic Trees Zdeněk Žabokrtský Otakar Smrž Center for Computational Linguistics Faculty of Mathematics and Physics Charles University in Prague from Constituency to Dependency

April 15, 2003Arabic Syntactic Trees: from Constituency to Dependency2 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, 2003Arabic Syntactic Trees: from Constituency to Dependency3 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, 2003Arabic Syntactic Trees: from Constituency to Dependency4 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

April 15, 2003Arabic Syntactic Trees: from Constituency to Dependency5 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

April 15, 2003Arabic Syntactic Trees: from Constituency to Dependency6 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

April 15, 2003Arabic Syntactic Trees: from Constituency to Dependency7 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...

April 15, 2003Arabic Syntactic Trees: from Constituency to Dependency8 Model Arabic Phrase II Sister-like co-ordination Conjunction of co-ordination Status constructus

April 15, 2003Arabic Syntactic Trees: from Constituency to Dependency9 Model Arabic Phrase III Non-expressed subject (?) Complex modality constructs Principal discrepancies between descriptions – both in topology and labeling

April 15, 2003Arabic Syntactic Trees: from Constituency to Dependency10 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.

April 15, 2003Arabic Syntactic Trees: from Constituency to Dependency11 Constituency Annotation

April 15, 2003Arabic Syntactic Trees: from Constituency to Dependency12 Dependency Annotation

April 15, 2003Arabic Syntactic Trees: from Constituency to Dependency13 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, 2003Arabic Syntactic Trees: from Constituency to Dependency14 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