Do Character-Level Neural Network Language Models Capture Knowledge of Multiword Expression Compositionality?
Paper · 2018 · Ali Hakimi Parizi and Paul Cook
Summary
The paper asks whether character-level recurrent language models encode how compositional a multiword expression (MWE) is, that is, how much its meaning follows from its parts. The authors train a character-level LSTM language model on roughly 100M-character samples of English and German Wikipedia. They feed each MWE, and each of its component words, through the model as a plain character string. The final hidden state serves as the vector. Compositionality is then scored with cosine similarity, in the style of Salehi et al. (2015): either a weighted mix of MWE–component similarities (comp1) or similarity to the sum of the component vectors (comp2). They evaluate on English noun compounds (ENC), English verb-particle constructions (EVPC) and German noun compounds (GNC).
Correlations with human ratings are modest but significant for ENC and for the particle side of EVPC. They are not significant for GNC or for the verb side of EVPC. All results stay well below word2vec-based baselines. The main appeal is practical. The method does not need MWE occurrences to be identified in a corpus, and it can score rare or unseen expressions.
Key points
- Default model: a TensorFlow char-RNN with a two-layer LSTM, one-hot characters and 128 hidden units (batch 20, learning rate 0.002, no dropout). Training data were 1% of the English and 2% of the German Wikipedia dumps (20 Jan 2018), cleaned with WP2TXT.
- Evaluation sets: ENC has 90 compounds (Reddy et al., 2011), EVPC has 160 verb-particle constructions (Bannard, 2006) and GNC has 244 compounds (von der Heide and Borgwaldt, 2009). Scores are Pearson's r against human ratings, with α = 0.7 for the noun-compound sets and 0.5 for EVPC.
- Pearson's r for comp1 and comp2:
- ENC: 0.239 and 0.286, both significant, compared with 0.717 for the word2vec baseline.
- EVPC particle: 0.313 and 0.301, both significant.
- EVPC verb and GNC: near zero or negative.
- On the 71 EVPC items that occur fewer than 5 times in training, particle correlations remain significant (0.327 and 0.308). Unseen English noun compounds, however, receive no significant prediction.
- Several variants gave no consistent gain over the default setup: a backward LSTM, a bi-directional LSTM, a plain RNN, a GRU, learned character embeddings of size 25 or 50, a larger batch, and dropout.
Interesting ideas
- I1. An expression's vector can be read directly from a character model's final state by spelling out the whole phrase, space included, which avoids corpus-level detection of that phrase.
- I2. Scoring each component's contribution separately, instead of one overall number, shows which part of a phrase keeps its literal meaning (here, the particle more than the verb).
- I3. Splitting the evaluation into attested, rare and unseen items shows where a model truly generalises and where it merely remembers.
- I4. The authors flag two practical limits: "gappy" expressions (with a slot inside) cannot simply be spelled out, and split verb-particle constructions had to be fed to the model in joined form.
For Mova
How these ideas could serve Mova, our small open language model — its files, stages and tests:
- I1 (world): Phrase vectors could be built this way for rare compounds missing from WordNet, giving a fallback signal on whether the compound should inherit its head's ontology class.
- I2 (frames): When mapping phrasal verbs to VerbNet frames, a per-component literalness estimate could decide whether the particle adds a directional or path role or whether the whole verb should be treated as a single lexical unit.
- I3 (learn): Evaluation reports could routinely break scores down by training frequency, used as a control alongside negative controls, so that gains on frequent items do not mask failure on unseen ones.
- I4 (tree): After UD parsing, compound:prt and similar relations could be used to rejoin split particles into a canonical string before any lexicon or compositionality lookup.
Institutions
Fields, topics and concepts
📚 Shelves 4The field of science this work belongs to (OpenAlex fields).Computer Science · 18,614 worksArtificial Intelligence · 17,965 worksArts and Humanities · 17,450 worksLanguage and Linguistics · 17,296 works
🧭 Topics 2Research subjects and languages the work is about.Language models & pretraining · 3,894 worksIdioms & multiword expressions · 222 works
Cite
Cite as Ali Hakimi Parizi and Paul Cook. 2018. Do Character-Level Neural Network Language Models Capture Knowledge of Multiword Expression Compositionality?. Proceedings of the Joint Workshop on Linguistic Annotation, Multiword Expressions and Constructions (LAW-MWE-CxG-2018).
@inproceedings{parizi2018do,
title = {{Do Character-Level Neural Network Language Models Capture Knowledge of Multiword Expression Compositionality?}},
author = {Ali Hakimi Parizi and Paul Cook},
booktitle = {Proceedings of the Joint Workshop on Linguistic Annotation, Multiword Expressions and Constructions (LAW-MWE-CxG-2018)},
year = {2018},
url = {https://aclanthology.org/W18-4920/}
}References
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