How did they obtain part-of-speech tags?
Using NLTK POS tagger
We report an implementation of a clinical information extraction tool that leverages deep neural network to annotate event spans and their attributes from raw clinical notes and pathology reports. Our approach uses context words and their part-of-speech tags and shape information as features. Then we hire temporal (1D) convolutional neural network to learn hidden feature representations. Finally, we use Multilayer Perceptron (MLP) to predict event spans. The empirical evaluation demonstrates that our approach significantly outperforms baselines.
In the past few years, there has been much interest in applying neural network based deep learning techniques to solve all kinds of natural language processing (NLP) tasks. From low level tasks such as language modeling, POS tagging, named entity recognition, and semantic role labeling BIBREF0 , BIBREF1 , to high level tasks such as machine translation, information retrieval, semantic analysis BIBREF2 , BIBREF3 , BIBREF4 and sentence relation modeling tasks such as paraphrase identification and question answering BIBREF5 , BIBREF6 , BIBREF7 . Deep representation learning has demonstrated its importance for these tasks. All the tasks get performance improvement via learning either word level representations or sentence level representations. In this work, we brought deep representation learning technologies to the clinical domain. Specifically, we focus on clinical information extraction, using clinical notes and pathology reports from the Mayo Clinic. Our system will identify event expressions consisting of the following components: The input of our system consists of raw clinical notes or pathology reports like below: And output annotations over the text that capture the key information such as event mentions and attributes. Table TABREF7 illustrates the output of clinical information extraction in details. To solve this task, the major challenge is how to precisely identify the spans (character offsets) of the event expressions from raw clinical notes. Traditional machine learning approaches usually build a supervised classifier with features generated by the Apache clinical Text Analysis and Knowledge Extraction System (cTAKES) . For example, BluLab system BIBREF8 extracted morphological(lemma), lexical(token), and syntactic(part-of-speech) features encoded from cTAKES. Although using the domain specific information extraction tools can improve the performance, learning how to use it well for clinical domain feature engineering is still very time-consuming. In short, a simple and effective method that only leverage basic NLP modules and achieves high extraction performance is desired to save costs. To address this challenge, we propose a deep neural networks based method, especially convolution neural network BIBREF0 , to learn hidden feature representations directly from raw clinical notes. More specifically, one method first extract a window of surrounding words for the candidate word. Then, we attach each word with their part-of-speech tag and shape information as extra features. Then our system deploys a temporal convolution neural network to learn hidden feature representations. Finally, our system uses Multilayer Perceptron (MLP) to predict event spans. Note that we use the same model to predict event attributes.