  Previous researchers have considered sentiment analysis as a document
classification task, in which input documents are classified into predefined
sentiment classes. Although there are sentences in a document that support
important evidences for sentiment analysis and sentences that do not, they have
treated the document as a bag of sentences. In other words, they have not
considered the importance of each sentence in the document. To effectively
determine polarity of a document, each sentence in the document should be dealt
with different degrees of importance. To address this problem, we propose a
document-level sentence classification model based on deep neural networks, in
which the importance degrees of sentences in documents are automatically
determined through gate mechanisms. To verify our new sentiment analysis model,
we conducted experiments using the sentiment datasets in the four different
domains such as movie reviews, hotel reviews, restaurant reviews, and music
reviews. In the experiments, the proposed model outperformed previous
state-of-the-art models that do not consider importance differences of
sentences in a document. The experimental results show that the importance of
sentences should be considered in a document-level sentiment classification
task.
