A Structured Vector Space Model for Word Meaning in Context
Summary
Standard semantic spaces give each lemma a single vector that averages over all its uses, so they cannot show how a word's sense shifts in context. Earlier composition approaches merge a target and its context word into one vector. These approaches ignore the syntactic relation between the two words (for example, "a horse draws" versus "draw a horse") and produce one shared result rather than a separate meaning for each word. Erk and Padó propose a structured vector space model (SVS). In SVS, a word is represented by a lexical vector plus one vector per syntactic relation, each encoding the word's selectional preferences (and inverse preferences) for that argument slot. To get a word's meaning in context, its lexical vector is combined with the context word's preference vector for the relation linking them.
The authors evaluate SVS on judging whether paraphrases fit a given context, using the M&L dataset and a subset of the SemEval Lexical Substitution data. SVS beats the Mitchell & Lapata (M&L) model on both. The gain is significant on the more realistic Lexical Substitution data, which suggests that syntax-aware expectations improve context-sensitive word meaning.
Key points
- Each word gets a lexical vector plus relation-specific preference vectors, such as subj, obj, and inverse relations like obj⁻¹, subj⁻¹, and comp⁻¹. Selectional preferences are computed as vectors from previously seen arguments.
- Experiment 2 uses three subsets of the Lexical Substitution data:
- V-SUBJ: verbs with subjects.
- V-OBJ: verbs with objects.
- N-OBJ: nouns as objects, 102 sentences.
- The task is framed as ranking pooled paraphrases and scored with SemEval's "out of ten" precision (P_OOT).
- SELPREF-POW (n=30) results:
- It scores 63.1, 55.8, and 56.9 P_OOT on the three subsets, compared with M&L at 50.3, 52.0, and 53.4.
- It is significantly better than M&L (p = 0.05) and highly significantly better than the target-only baseline (p < 0.01).
- Baselines: target-only scores 47–50 and a random baseline scores 22%. A "selpref only" baseline already beats M&L on V-SUBJ and N-OBJ.
- In the SYN space, vectors with raw frequency components modeled the data, but PMI-weighted vectors did not. On the M&L dataset, SVS was better than M&L but not significantly.
Interesting ideas
- I1. Relation-indexed expectation vectors. Storing a separate "typical filler" vector per syntactic relation lets the same word pair be interpreted differently depending on its dependency relation. This approach could transfer to dependency-parsed corpora, such as UD treebanks for Ukrainian.
- I2. Separate in-context vectors for each word. The model produces an adapted vector for each word rather than one merged phrase vector. Sentence structure can then stay in an explicit parse while the vectors carry only lexical meaning, which is a useful separation for entailment or inference pipelines.
- I3. Ablation baselines that isolate each signal. "Target only" uses no context and "selpref only" uses the context word's expectations alone. Comparing against these shows exactly where the gains come from, and the same diagnostic design suits any context-modeling evaluation.
- I4. Lenient top-10 evaluation for sparse gold data. Paraphrase annotations are incomplete, so scoring the model's ten best guesses weighted by annotator frequency avoids penalizing valid but unlisted answers. This is relevant whenever gold sets for substitution or synonym tasks are crowd-sourced and patchy.
- I5. Paraphrase fit as a test of inference rules. Judging whether a paraphrase suits a context can double as a check on when a paraphrase-based inference rule applies. This links lexical semantics evaluation to downstream Textual Entailment.
Cited by
- Distributional Memory: A General Framework for Corpus-Based Semantics
- Text: now in 2D! A framework for lexical expansion with contextual similarity
- Experience Grounds Language
- Analysing Lexical Semantic Change with Contextualised Word Representations
- A Structured Distributional Semantic Model for Event Co-reference
- Revisiting Selectional Preferences for Coreference Resolution
- Multilingual Models for Compositional Distributed Semantics
- Improving Word Representations via Global Context and Multiple Word Prototypes
- Deep Unordered Composition Rivals Syntactic Methods for Text Classification
- A Convolutional Neural Network for Modelling Sentences
- Improved Statistical Machine Translation Using Monolingually-Derived Paraphrases
Cite
@inproceedings{erk2008structured,
title = {{A Structured Vector Space Model for Word Meaning in Context}},
author = {Erk, Katrin and Padó, Sebastian},
booktitle = {Proceedings of the 2008 Conference on Empirical Methods in Natural Language Processing},
year = {2008},
doi = {10.3115/1613715.1613831},
url = {https://doi.org/10.3115/1613715.1613831}
}References
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