Comparing PTB and UD information for PDTB discourse connective identification
What it is about
Deciding whether a connective candidate (when, and, since, instead) is used as a discourse connective is the first step of shallow discourse parsing. Classic feature-based classifiers on PDTB used Penn Treebank constituents: the connective string alone already gives about 86% accuracy, and syntactic context (the category covering the connective, its parent and siblings, whether the right sibling contains a VP; later the neighbouring words and their tags, and the path to the root) brings it to about 96–99%. The authors reproduce Pitler & Nenkova 2009, Lin et al. 2014 and Li et al. 2016 with logistic regression, then replace the PTB information by Universal Dependencies (coarser tags, dependency relations, automatically parsed). UD information turns out to be enough: with predicted UD parses they obtain slightly better results than with gold PTB tags, which makes the method usable wherever only UD parsers exist.
Ideas
- I1. Write the connective-vs-non-connective decision in Mova as explicit UD rules rather than a learned classifier, since UD alone suffices: a subordinator counts when it is
markof anadvcl(oradvmodof anadvclfor when/where), a coordinator when it isccof a conjoined clause or VP, an adverbial (instead, then, so, however) when it isadvmodof the main predicate at clause edge; when/where inside a relative or a wh-question are not connectives. Each rule is a named test that prints why. Measure link precision on the frame bench and against GUM's eRST discourse markers on dev (evaluation only). - I2. Use the paper's feature set as a check-list for the cases rules miss: the token before the connective, the dependency relation of the connective and of its head, and whether the head is a verb. A small perceptron over these, trained on licence-clean silver (teacher-labelled tale sentences), can back up the rules for the ambiguous and, as, since, so; report it only if it beats the rules on held-out silver.
- I3. Measure on SLM trees as well as gold trees: the paper's point is that predicted UD parses do not hurt. The frame bench already runs on SLM trees; split link errors into parser errors (wrong
advcl/mark) and rule errors.
For Mova
36. Discourse relations and coherence §6 (connectives and their syntax), §10, §11.1. Code: prag/src/frames.rs (connective tests), Subordinating conjunctions — mark. Measures: frame bench cause/next precision, connective precision vs GUM eRST markers on dev, error split by tree source.
Cite
@inproceedings{han2020comparing,
title = {{Comparing PTB and UD information for PDTB discourse connective identification}},
author = {Han, Kelvin and Leavitt, Phyllicia and Balard, Srilakshmi},
booktitle = {Actes de la 6e conférence conjointe Journées d'Études sur la Parole (JEP, 33e édition), Traitement Automatique des Langues Naturelles (TALN, 27e édition), Rencontre des Étudiants Chercheurs en Informatique pour le Traitement Automatique des Langues (RÉCITAL, 22e édition). Volume 3 : Rencontre des Étudiants Chercheurs en Informatique pour le TAL},
year = {2020},
url = {https://aclanthology.org/2020.jeptalnrecital-recital.10/}
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