CSE 5525 Homework 3: CNNs and Tagging
Alan Ritter
1 Convolutional Neural Networks for Text Clas- sification (5 points)
For the first part of this assignment, you will implement a convolutional neural network for sentiment classification using the IMDB movie review dataset provided in homework #2. First, copy the starter code from the file FFNN.py to a new file CNN.py, and use this as a starting point. Create a network containing an embedding layer, a single convolutional layer, followed by a pooling layer that does max-pooling over time, a nonlinearity (e.g, ReLU or Tanh) a linear layer and a softmax. You should make use of unigram, bigram and trigram filters. To do this, you should make use of the following classes in Pytorch (see documentaiton on the Pytorch Website):
nn.Conv1d
nn.MaxPool1d
Your report should clearly explain hyperparameters you used (embedding dimensions, number of filters, etc). You should report performance on the de- velopment and test sets (aclImdb small) for both your CNN and feedforward neural network implementations.
hints: You will most likely need to use the functions torch.unsqueeze and torch.view. You probably also need to use at least 100-200 convolu- tional filters of each size in order to get good performance.
2 Structured Perceptron Tagger (15 points)
In the second part of the assignment you will implement the structured per- ceptron and Viterbi algorithms for part-of-speech tagging. Then you will
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experiment with your trained models on a small dataset of tweets annotated with parts-of-speech and named entities. These experiments will explore the question of how well part of speech taggers perform when applied to do- mains other than for which they were trained. For example, how well does a Wall Street Journal trained part-of-speech tagger perform when applied on Twitter?
We provide you with starter Python code to help read in the data and evaluate the results of your models predictions. You are strongly encouraged to make use of the provided code. If you really prefer to implement every- thing from scratch for some reason, please talk to the instructor first. Your submitted code should run on the command line in a unix-like environment (e.g. Linux, OSX, Cygwin).
The experiments required to complete the assignment will take some time to run, so it is highly recommended to start early. We recommend you read through this entire document and run the sample code before getting started.
We have provided an evaluation script to train your models and generate predictions on the test data as follows:
> #Trains a part-of-speech tagger on the provided Twitter training set
> bash eval.sh twitter
> #Trains a part-of-speech tagger on the provided penn treebank data
> bash eval.sh ptb
#Trains a part-of-speech tagger on the provided IRC chat data
> bash eval.sh nps
Your models predictions on the test data will be output into the direc- tory, eval/. You can check the accuracy of your model on the test data by using the provided scripts accuracy.py for POS-tagging and the Perl script conlleval.pl for named entity recognition.
When you first run the starter code, the tagger will always predict every word is a noun. You will need to implement the viterbi algorithm for decoding in addition to parameter updates analogous to the perceptron algorithm in Homework #2.
Words Most Frequent Tag Baseline (2 points)
Before getting started with implementing the perceptron tagger, write a sim-
ple program to implement the following baseline. First count the number of
times each word occurs with each tag in the training dataset (data/twitter train universal.txt)
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Now generate an output file (using the same format as the training data) that predicts the tag of each word using the following heuristic: simply tag each word in the test dataset (data/twitter test universal.txt) with the tag that appears most frequently in the training dataset (breaking ties arbitrar- ily). Tag all the unseen words in the test set as nouns. Report your accuracy on the test data using the provided script like so:
> python accuracy.py mft_baseline.out data/twitter_test_universal.txt
Viterbi Algorithm (6 points)
Implement the Viterbi Algorithm for a bigram perceptron tagger. The pro- vided code in Data.py will read in the provided training data. You should make use of log-scores (unnormalized log probabilities) each multiplication in Viterbi should be replaced with addition, and unnormalized probabili- ties are simply dot products of feature vectors and weights. Note: you will need to complete the next part of the assignment before you can test if your implementation is properly working.
The method you will need to implement is ViterbiTagger.Viterbi. Be- fore you do this, the classifier always predicts Noun.
Structured Perceptron (4 points)
Next, implement the structured perceptron algorithm. For this you will need to modify Tagger.Train. Include parameter averaging as in Homework #2. Report your performance (accuracy) training and testing on the Twitter data.
Cross-Domain Experiments (2 points)
Next, try training your POS tagger in each of the following scenarios and report accuracy:
Train on the provided penn-treebank data and test on Twitter. Train on the provided IRC-chat data and test on Twitter.
Train on all the data (irc + ptb + twitter) and test on Twitter. What can you say about the performance of part-of-speech taggers when
they are applied on text outside their training domain? 3
Extra Credit: Named Entity Recognition (2 points)
Train your tagger on the provided named entity recognition dataset twitter ner train.txt and report precision, recall and F1 on twitter ner test.txt using the pro-
vided script conlleval.pl. Next, add additional features to the tagger
specifically for the named entity recognition task, and report performance.
Commonly used features for named entity recognition include lists of first and last names.1. Lists of companies, products, etc can be scraped from various places on the web, such as Wikipedia.2.
1 http://www.census.gov/topics/population/genealogy/data/1990_census/ 1990_census_namefiles.html
2 https://en.wikipedia.org/wiki/List_of_companies_of_the_United_States 4
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