# Formal Constraints on Dependency Syntax

arXiv: https://arxiv.org/abs/2604.04542 · HTML: https://mlsanity.com/paper/2604.04542/

## Key facts

- No citing papers in the map yet (data through 14 Oct 2026).
- Builds on 14 of its 54 references that are in the map.
- First posted on arXiv 6 Apr 2026.

## Builds on (most cited first, 14 of 14)

- [Deep Biaffine Attention for Neural Dependency Parsing](https://mlsanity.com/paper/1611.01734/) (2016)
- [Viable Dependency Parsing as Sequence Labeling](https://mlsanity.com/paper/1902.10505/) (2019)
- [Left-to-Right Dependency Parsing with Pointer Networks](https://mlsanity.com/paper/1903.08445/) (2019)
- [The optimality of syntactic dependency distances](https://mlsanity.com/paper/2007.15342/) (2020)
- [Bracketing Encodings for 2-Planar Dependency Parsing](https://mlsanity.com/paper/2011.00596/) (2020)
- [Span-based discontinuous constituency parsing: a family of exact chart-based algorithms with time complexities from O(n^6) down to O(n^3)](https://mlsanity.com/paper/2003.13785/) (2020)
- [Prague Dependency Treebank -- Consolidated 1.0](https://mlsanity.com/paper/2006.03679/) (2020)
- [4 and 7-bit Labeling for Projective and Non-Projective Dependency Trees](https://mlsanity.com/paper/2310.14319/) (2023)
- [Are crossing dependencies really scarce?](https://mlsanity.com/paper/1703.08324/) (2017)
- [Memory limitations are hidden in grammar](https://mlsanity.com/paper/1908.06629/) (2019)
- [Crossings as a side effect of dependency lengths](https://mlsanity.com/paper/1508.06451/) (2015)
- [Global Transition-based Non-projective Dependency Parsing](https://mlsanity.com/paper/1807.01745/) (2018)
- [Hexatagging: Projective Dependency Parsing as Tagging](https://mlsanity.com/paper/2306.05477/) (2023)
- [Improving Coverage and Runtime Complexity for Exact Inference in Non-Projective Transition-Based Dependency Parsers](https://mlsanity.com/paper/1804.10615/) (2018)

## Abstract (arXiv)

Dependency syntax represents the structure of a sentence as a tree composed of dependencies, i.e., directed relations between lexical units. While in its more general form any such tree is allowed, in practice many are not plausible or are very infrequent in attested language. This has motivated a search for constraints characterizing subsets of trees that better fit real linguistic phenomena, providing a more accurate linguistic description, faster parsing or insights on language evolution and human processing. Projectivity is the most well-studied such constraint, but it has been shown to be too restrictive to represent some linguistic phenomena, especially in flexible-word-order languages. Thus, a variety of constraints have been proposed to seek a realistic middle ground between the limitations of projectivity and the excessive leniency of unrestricted dependency structures.