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Ontology-Aware Token Embedding and LSTM Encoder

This repository contains a Keras implementation of WordNet grounded context sensitive token embeddings, described in the paper Ontology-Aware Token Embeddings for Prepositional Phrase Attachment. Primarily, we implement two Keras layers here: OntologyAwareEmbedding and OntoAttentionLSTM, which (in most cases) will be used together.

Background

The idea behind WordNet grounding is to represent words as a distribution over their senses and possible hypernyms from WordNet. That is, given a word pool as a noun, WordNet 3.1 identifies 9 senses of the word:

  • pool.n.01: An excavation
  • pool.n.02: A small lake
  • pool.n.03: An organization of people or resources
  • ...

For each of these senses, WordNet also defines hypernyms (generalizations) in order, like:

  • pool.n.01: excavation.n.01, artifact.n.01, ...
  • pool.n.02: lake.n.01, body_of_water.n.01, ...
  • pool.n.03: organization.n.01, social_group.n.01, ...

We represent a token pool as a weighted average of the representations of a fixed number of its hyperyms, coming from a fixed number of its senses.

The weights in the weighted average depend on the context, thus making our word representations context-sensitive (or formally token-level representations instead of type-level). For example, the distribution of weights for the word pool in the following sentence:

Swimming is not allowed in this pool.

is different from those in the following sentence:

I managed to find a car pool.

The computation of this context sensitive weight distribution is tied to the computation that happens in the encoder (LSTM in our case).

Installation

Clone this repository and run

pip install -r requirements.txt

The code is written in Python 2.7 and depends on Keras 1.2.1.

Using OntoLSTM in your network

The input needs to be POS tagged. Look at data/test_data.tsv as an example. The file contains labels in the first column and POS-tagged sentences in the second. These sentences were tagged using Stanford POS tagger.

test_ontolstm.py shows a simple implementation of a binary classifier using OntoLSTM as the encoder. Try running the following to test your installation.

python test_ontolstm.py

Reproducing PP Attachment results from ACL 2017 paper

Set up the data

Download the train and test data created by Yonatan Belinkov, available here, and set them up in the same format as the sample test data, with labels indicating the index of the correct head words. The dataset comes with POS tags of head words, so you will not need a POS tagger for this. Concatenate the preposition and the dependent of the preposition at the end of the set of head words. Your train and test sets should have tab separated lines that look like this:

4  succeed_VB arbitrator_NN decision_NN made_VB in_PP dispute_NN

where 4 indicates the label (i.e. the 4th word, made is the head word to which the PP in dispute attaches to). Note that all verbs are indicated as VB and all nouns as NN. We do not follow the Penn Tree Bank POS tag set here. In fact, OntoLSTM needs a coarse distinction among nouns, verbs, adjectives and adverbs, and not more since those are the word classes available in WordNet. See the method get_hypernyms_sentence in index_data.py for the logic.

Obtain synset embeddings

We got synset vectors by running AutoExtend on GloVe, and used these to initialize our synset embeddings. You can download them here. Alternatively, you can build them yourself: Download AutoExtend and run it on GloVe vectors, to obtain synset vectors. We use the 100d vectors. Make sure to use WordNet 3.1 as the ontology for AutoExtend.

Train and test OntoLSTM PP

Run

python2.7 model_pp_attachment.py --train_file TRAIN.tsv --test_file TEST.tsv --embedding_file autoextend_glove_100d.txt.gz --embed_dim 100 --tune_embedding --bidirectional --onto_aware --use_attention --num_senses 3 --num_hyps 5 --embedding_dropout 0.5 --encoder_dropout 0.2

That's it! This should also save the best trained model on your disk.

Contact

If you use OntoLSTM in your work, I would love to hear about it. Please feel free to contact me if you run into any issues using it or even with general feedback.

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Keras implementation of ontology aware token embeddings

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