| Challenge: | Discontinuous parsing is more challenging than continuous parsers because children can group with syntactic cousins in the sentence rather than its two adjacent neighbors. |
| Approach: | They extend a pair of combinator-based constituency parsers into a discontinuous pair . they use a swap action and biaffine attention to iteratively compose constituent vectors from word embeddings without any grammar constraints. |
| Outcome: | The proposed parsers achieve state-of-the-art discontinuous accuracy with a significant speed advantage over continuous parsing. |
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Reorder and then Parse, Fast and Accurate Discontinuous Constituency Parsing (2022.emnlp-main)
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| Challenge: | Discontinuous constituency parsing is still being developed for its efficiency and accuracy are far behind its continuous counterparts. |
| Approach: | They propose to transform a discontinuous constituent tree into a pseudo-continuous one by reordering words in the sentence. |
| Outcome: | The proposed method can transform a discontinuous constituent tree into a pseudo-continuous one by parsing and performing actions on three classical discontinuous constituency treebanks. |
Discontinuous Constituency Parsing with a Stack-Free Transition System and a Dynamic Oracle (N19-1)
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| Challenge: | Discontinuous constituency trees are derivations of Linear Context-Free Rewriting Systems (LCFRS), which makes them much harder to parse. |
| Approach: | They propose a transition system that uses a set of parsing items with constant-time random access instead of storing subtrees in a stack . |
| Outcome: | The proposed system constructs a discontinuous constituency tree in 4n–2 transitions for a sentence of length n. |
Neural Combinatory Constituency Parsing (2021.findings-acl)
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| Challenge: | Existing approaches to constituency parsing are based on symbolic engineering, but they are simplified by their adaptive distributed representation. |
| Approach: | They propose two fast combinatory models for constituency parsing: binary and multibranching. |
| Outcome: | The proposed models achieve an F1 score of 92.54 on Penn Treebank, speeding at 1327.2 sents/sec. |
Span-based discontinuous constituency parsing: a family of exact chart-based algorithms with time complexities from O(nˆ6) down to O(nˆ3) (2020.emnlp-main)
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| Challenge: | a novel chart-based parser for discontinuous constituency trees is proposed for span-based span parsing . it can process discontinuous constituent trees of block degree two, including ill-nested structures . |
| Approach: | They propose a chart-based algorithm for span-based parsing of discontinuous constituency trees . they build variants with smaller search spaces and time complexities ranging from O(n6) down to O(N3) . |
| Outcome: | The proposed algorithm can process 98% of constituents in linguistic treebanks while having the same complexity as continuous constituency parsers. |
Don’t Parse, Choose Spans! Continuous and Discontinuous Constituency Parsing via Autoregressive Span Selection (2023.acl-long)
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| Challenge: | Constituency parsing is a fundamental task in natural language processing, having many applications in downstream tasks such as language modeling. |
| Approach: | They propose a simple and unified approach for both continuous and discontinuous constituency parsing via autoregressive span selection. |
| Outcome: | The proposed model can predict all possible continuous and discontinuous constituency trees without sacrificing data coverage and without expensive chart-based parsing algorithms. |
BERT-Proof Syntactic Structures: Investigating Errors in Discontinuous Constituency Parsing (2021.findings-acl)
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| Challenge: | Recent results show that pretrained language models can be used for many tasks with high accuracy and high performance. |
| Approach: | They propose two methods for automatically analysing discontinuous parsers' errors. |
| Outcome: | The proposed methods characterize errors of a state-of-the-art transition-based discontinuous parser and provide an overview of the contribution of BERT to this task. |
Training a Swedish Constituency Parser on Six Incompatible Treebanks (2020.lrec-1)
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| Challenge: | Syntactic parsing is a widely used intermediate step in several natural language processing tasks. |
| Approach: | They propose to use a function-tagged constituent treebank for Swedish which includes discontinuous constituents to improve the accuracy. |
| Outcome: | The proposed parser can be trained on additional treebanks that use other annotation models. |
Reducing Discontinuous to Continuous Parsing with Pointer Network Reordering (2021.emnlp-main)
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| Challenge: | Existing discontinuous constituent parsers are slow and lack accuracy and speed . however, discontinuous parsing can be solved by any off-the-shelf continuous parser . |
| Approach: | They propose to reduce discontinuous constituent parsing to a continuous problem by reordering tokens. |
| Outcome: | The proposed method is on par with state-of-the-art methods but considerably faster. |
An Empirical Study of Building a Strong Baseline for Constituency Parsing (P18-2)
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| Challenge: | Sequence-to-sequence models have been used for natural language generation tasks such as machine translation and summarization. |
| Approach: | They propose to build a strong baseline based on general purpose sequence-to-sequence models for constituency parsing. |
| Outcome: | The proposed model outperforms existing models in natural language generation tasks without any explicit task-specific knowledge or architecture of constituent parsing. |
Challenges to Open-Domain Constituency Parsing (2022.findings-acl)
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| Challenge: | Existing findings on cross-domain constituency parsing are only made on a limited number of domains. |
| Approach: | They manually annotate a high-quality constituency treebank containing five domains and analyze challenges to open-domain constituency parsing using a set of linguistic features. |
| Outcome: | The proposed model significantly improves the performance of the proposed model on the domain-variant features. |