---
title: "When Are Tree Structures Necessary for Deep Learning of"
description: "Recursive (tree-structured) neural networks build sentence representations by composing words… 42 references, cited by 59 papers here."
authors: ["Jiwei Li", "Thang Luong", "Dan Jurafsky", "Eduard Hovy"]
year: 2015
venue: "Proceedings of the 2015 Conference on Empirical Methods in Natural Language Processing"
source: "https://aclanthology.org/D15-1278/"
doi: "10.18653/v1/d15-1278"
licence: "CC BY-NC-SA 3.0 (ACL Anthology, before 2016)"
licence_url: "https://creativecommons.org/licenses/by-nc-sa/3.0/"
summary_licence: "Elamur Cosmic License"
canonical: "https://research.elamur.ai/free/en/papers/li-2015-when-are-tree-structures-necessary/"
---
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# When Are Tree Structures Necessary for Deep Learning of Representations?

**Authors:** [Jiwei Li](https://md.research.elamur.ai/free/en/authors/jiwei-li/), [Thang Luong](https://md.research.elamur.ai/free/en/authors/thang-luong/), [Dan Jurafsky](https://md.research.elamur.ai/free/en/authors/dan-jurafsky/) and [Eduard Hovy](https://md.research.elamur.ai/free/en/authors/eduard-hovy/) · **Year:** 2015 · **Venue:** [Proceedings of the 2015 Conference on Empirical Methods in Natural Language Processing](https://md.research.elamur.ai/free/en/venues/emnlp/) ([EMNLP 2015](https://md.research.elamur.ai/free/en/venues/emnlp/2015/)) · **Publisher:** [Association for Computational Linguistics](https://md.research.elamur.ai/free/en/publishers/association-for-computational-linguistics/) · **Licence:** [CC BY-NC-SA 3.0 (ACL Anthology, before 2016)](https://creativecommons.org/licenses/by-nc-sa/3.0/)

**Links:** [Publisher's page](https://aclanthology.org/D15-1278/) · [PDF](https://aclanthology.org/D15-1278.pdf) · [DOI 10.18653/v1/d15-1278](https://doi.org/10.18653/v1/d15-1278) · [OpenAlex](https://openalex.org/W1816079941)

**Citations:** 207 citations (OpenAlex, 2026-10-14) · [59](https://md.research.elamur.ai/free/en/papers/li-2015-when-are-tree-structures-necessary/cited-by/) in our library, of the 141,840 papers whose bibliographies we read

## Summary
Recursive (tree-structured) neural networks build sentence representations by composing words along a syntactic parse, but it was unclear which tasks actually benefit from this structure compared with simpler sequential models. Li, Luong, Jurafsky and Hovy run a controlled comparison of tree-based models against unidirectional and bidirectional recurrent models, in both plain and LSTM variants. They test five setups spanning four task areas: sentiment on the Pang et al. (2002) data and the Stanford Sentiment Treebank, question–phrase matching on UMD-QA, relation classification on SemEval-2010, and discourse relation identification on the RST data. All models share one training regime: a single composition layer, AdaGrad with minibatches, and identical initialization. Trees give a clear advantage mainly when distant headwords must be linked, as in relation extraction, and on long inputs. A recurrent model that splits sentences at punctuation into clause-like pieces and then combines them largely closes that gap. The study clarifies when parsing is worth its cost and points to concrete ways to improve sequence models.

## Key points
- Models compared: standard tree vs. sequence vs. bi-sequence models, plus Tree LSTM vs. LSTM vs. bidirectional LSTM. Significance is checked with a bootstrap test at the 0.05 level.
- On the Stanford Sentiment Treebank, recurrent models are trained on 215,154 phrase examples. Evaluation covers 82,600 phrase-level and 2,210 root-level instances. Trees help slightly at the root level but hardly at the phrase level, and bidirectional recurrent models mostly erase the difference.
- On the Pang et al. dataset, where labels appear only at the top of long sequences, tree and sequence models show no significant difference.
- On RST relation identification, accuracies are close:
  - Standard models: tree 0.568, sequence 0.572, bi-sequence 0.578.
  - LSTM models: tree 0.564, sequence 0.563, bi-LSTM 0.575, the only significant gain (p = 0.040).
- On UMD-QA, intermediate recurrent outputs carry evidence as useful as parse-tree nodes, even though they are not linguistically meaningful units.

*Our summary of the paper, in our own words — not its text. The work belongs to its authors; read it at the links above.*

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## Cite

Cite as: Jiwei Li, Thang Luong, Dan Jurafsky and Eduard Hovy. 2015. When Are Tree Structures Necessary for Deep Learning of Representations?. Proceedings of the 2015 Conference on Empirical Methods in Natural Language Processing.

The paper itself, not this page. BibTeX from the library's record of the work.

```bibtex
@inproceedings{li2015when,
  title = {{When Are Tree Structures Necessary for Deep Learning of Representations?}},
  author = {Jiwei Li, Thang Luong, Dan Jurafsky and Eduard Hovy},
  booktitle = {Proceedings of the 2015 Conference on Empirical Methods in Natural Language Processing},
  year = {2015},
  doi = {10.18653/v1/d15-1278},
  url = {https://doi.org/10.18653/v1/d15-1278}
}
```

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## References

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*Updated 24 October 2026*