Neural models achieved considerable improvement for many natural language processing tasks, but they offer little transparency, and interpretability comes at a cost. In some domains, automated predictions without justifications have limited applicability. Recently, progress has been made regarding single-aspect sentiment analysis for reviews, where the ambiguity of a justification is minimal. In this context, a justification, or mask, consists of (long) word sequences from the input text, which suffice to make the prediction. Existing models cannot handle more than one aspect in one training and induce binary masks that might be ambiguous. In our work, we propose a neural model for predicting multi-aspect sentiments for reviews and generates a probabilistic multi-dimensional mask (one per aspect) simultaneously, in an unsupervised and multi-task learning manner. Our evaluation shows that on three datasets, in the beer and hotel domain, our model outperforms strong baselines and generates masks that are: strong feature predictors, meaningful, and interpretable.
This paper proposes a neural model for multi-aspect sentiment of reviews. Apart from sentiment classification, the architecture is able to return a mask for each aspect highlighting the sequences of words used to make the sentiment prediction for that aspect. This improves the interpretability of the model. The aspects are fixed and the training set requires a multi-labeled dataset with one binary positive/negative label per aspect.
The network architecture is mostly standard: a text review is turned into a list of word embeddings which are fed through a trainable masker outputting one mask per aspect, essentially "selecting" a different set of words (embeddings) per aspect. From here on, a standard encoder can be used (the authors end up using a CNN with max-pooling but LSTM or other could be used), followed by a classification step (standard MLP) outputting a sentiment score per aspect. A couple tricks are used to make the masks converge to something meaningful by adding regularization terms to control the number of selected words and encouraging consecutive words to be selected.
I'm leaning toward rejection partly due to the limited novelty in the approach but mainly due to the experimental evaluation section which requires improvements.
- High aspect correlation baseline: the average aspect correlation across reviews in the training set is high (that is, if one aspect is positive, most aspects will be and viceversa). A natural baseline to include is the optimal "no-aspect" decision boundary: in other words, if for each review we were given the majority rating across aspects (is this review mostly positive or negative) and were able to predict this always correctly, what would the macro-aspect F1 score be if we were to simply predict that label to all aspect of that review?
- Please quantify how much does your model rely on this aspect correlation. For example, if you were to sort the reviews in the validation set by their aspect correlation, and chart the F1 score as a function of the prefix of this sorted dataset what would we see? This would be especially telling when comparing the different baselines and classifiers again each other in this chart.
- SVM: you mentioned not running it on the larger datasets due to lengthy training time. I would suggest including NB-SVM implemented with logistic regression rather than actual SVM since it's always a great baseline and fast to compute (in "Baselines and Bigrams: Simple, Good Sentiment and Topic Classification").
- The final model that ends up giving the best results is really a 2-step pipeline (rather than end-to-end trainable) and requires training twice: once to learn the masks and once to actually train the rest of the network after the word embeddings are extended with the masks.