# A Transition-Based Directed Acyclic Graph Parser for UCCA

## TL;DR

This paper introduces the first parser for UCCA, a cross-linguistic semantic framework, capable of handling complex DAG structures, discontinuities, and non-terminal nodes, advancing semantic parsing technology.

## Contribution

It presents a novel transition-based parser with a unique transition set and bidirectional LSTM features, supporting complex DAG structures in semantic parsing.

## Key findings

- Successfully parses UCCA structures with reentrancy and discontinuities
- Handles non-terminal nodes representing complex semantic units
- Offers a parser architecture applicable to other semantic DAGs

## Abstract

We present the first parser for UCCA, a cross-linguistically applicable framework for semantic representation, which builds on extensive typological work and supports rapid annotation. UCCA poses a challenge for existing parsing techniques, as it exhibits reentrancy (resulting in DAG structures), discontinuous structures and non-terminal nodes corresponding to complex semantic units. To our knowledge, the conjunction of these formal properties is not supported by any existing parser. Our transition-based parser, which uses a novel transition set and features based on bidirectional LSTMs, has value not just for UCCA parsing: its ability to handle more general graph structures can inform the development of parsers for other semantic DAG structures, and in languages that frequently use discontinuous structures.