Shared Tasks of the 2015 Workshop on Noisy User-generated Text: Twitter Lexical Normalization and Named Entity Recognition
Summary
This paper reports on the two shared tasks organized with the W-NUT 2015 workshop: lexical normalization of English tweets and named entity recognition (NER) on Twitter. Earlier normalization research relied mostly on unsupervised or semi-supervised methods, which were tested on small hand-labelled sets, so it was hard to compare them. To address this, the organizers built a much larger annotated corpus. It covers one-to-one, one-to-many and many-to-one word mappings, and it includes non-standard tokens whose spelling happens to match a real word.
Ten teams took part in normalization. Systems were split into constrained and unconstrained tracks according to which resources they used. Eight teams entered the NER task, which had 10 entity types. The best normalization system reached an F1 of 0.8421 in the constrained track, which suggests that model quality mattered more than extra data. In NER, the ousia system used entity linking and clearly outperformed the other entries. Its score approached the level of agreement between human annotators.
These datasets and results became reference points for processing noisy social-media text.
Key points
- Normalization corpus:
- Tweets were collected in May 2014 and filtered with langid.py, then tokenized with the CMU-ARK tokeniser.
- The final corpus has 4,917 tweets, split into 2,950 for training and 1,967 for testing.
- Each tweet was labelled by two annotators out of a pool of 12 at IBM Research Australia, and disagreements were adjudicated.
- Average Cohen's κ was 0.5854.
- Lexicon:
- The boundary between standard and non-standard words was set by the SCOWL lexicon, using American spelling at the 70% size level, for 165,458 words in total.
- Tweets with fewer than two tokens outside this lexicon were discarded so that the annotated data would contain plenty of normalization cases.
- Normalization results:
- There were 6 constrained and 5 unconstrained submissions; one team entered both tracks.
- The winner scored P 0.9061, R 0.7865 and F1 0.8421.
- Neural networks performed well in the constrained track, while CRF- and lexicon-based systems did well in the unconstrained one.
- NER results:
- ousia scored 56.41 F1 with entity types and 70.63 F1 for segmentation only, against baseline scores of 31.97 and 49.88.
- NLANGP came second with typed F1 51.40.
- Common NER techniques:
- Most teams used linear-chain CRFs together with Brown clusters and word embeddings.
- Less common designs included a semi-Markov MIRA tagger (nrc), a feature-free feed-forward network over word2vec embeddings (multimedialab), and differential-evolution feature selection (iitp).
Interesting ideas
- I1. Fix the "standard word" boundary with a lexicon: Whether a word counts as standard is a matter of opinion. The organizers avoided endless debate by treating membership in one fixed dictionary as the definition. This makes annotation reproducible and could work for normalizing noisy Ukrainian or Surzhyk text.
- I2. Pre-filter for annotation density: Only tweets with at least two out-of-lexicon tokens were kept. This means annotators spend their time on informative examples, at the cost of some sampling bias. It is a cheap way to stretch a small annotation budget.
- I3. Constrained vs. unconstrained tracks: Splitting submissions by resource use shows whether gains come from the model or from extra data. Here, a constrained system won, a useful lesson when choosing between more data and a better model.
- I4. Use entity linking for NER: ousia linked candidate mentions to a knowledge base. It then used facts about the linked entity, such as its popularity, its classes, and how likely it is to appear in the given context, as classifier features. This approach could help NER in low-resource languages that have a Wikipedia-style knowledge base.
- I5. Down-weight older training data: USFD gave less weight to training examples that were far in time from the test data, to handle concept drift. This is relevant for any fast-changing social-media or news stream.
Cited by
- TweetEval: Unified Benchmark and Comparative Evaluation for Tweet Classification
- SemEval-2020 Task 9: Overview of Sentiment Analysis of Code-Mixed Tweets
- A Survey on Recent Advances in Named Entity Recognition from Deep Learning models
Cite
@inproceedings{baldwin2015shared,
title = {{Shared Tasks of the 2015 Workshop on Noisy User-generated Text: Twitter Lexical Normalization and Named Entity Recognition}},
author = {Baldwin, Timothy and Marneffe, Marie Catherine de and Han, Bo and Kim, Young-Bum and Ritter, Alan and Xu, Wei},
booktitle = {Proceedings of the Workshop on Noisy User-generated Text},
year = {2015},
doi = {10.18653/v1/w15-4319},
url = {https://doi.org/10.18653/v1/w15-4319}
}References
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