Abstract: This paper presents Senti17 system which uses ten convolutional neural networks (ConvNet) to assign a sentiment label to a tweet. The network consists of a convolutional layer followed by a fully-connected layer and a Softmax on top. Ten instances of this network are initialized with the same word embeddings as inputs but with different initializations for the network weights. We combine the results of all instances by selecting the sentiment label given by the majority of the ten voters. This system is ranked fourth in SemEval-2017 Task4 over 38 systems with 67.4%

Introduction: Polarity classification is the basic task of sentiment analysis in which the polarity of a given text should be classified into three categories: positive, negative or neutral. In Twitter where the tweet is short and written in informal language, this task needs more attention. SemEval has proposed the task of Message Polarity Classification in Twitter since 2013, the objective is to classify a tweet into one of the three polarity labels BIBREF0 . We can remark that in 2013, 2014 and 2015 most best systems were based on a rich feature extraction process with a traditional classifier such as SVM BIBREF1 or Logistic regression BIBREF2 . In 2014, kimconvolutional2014 proposed to use one convolutional neural network for sentence classification, he fixed the size of the input sentence and concatenated its word embeddings for representing the sentence, this architecture has been exploited in many later works. severynunitn:2015 adapted the convolutional network proposed by kimconvolutional2014 for sentiment analysis in Twitter, their system was ranked second in SemEval-2015 while the first system BIBREF3 combined four systems based on feature extraction and the third ranked system used logistic regression with different groups of features BIBREF2 . In 2016, we remark that the number of participations which use feature extraction systems were degraded, and the first four systems used Deep Learning, the majority used a convolutional network except the fourth one BIBREF4 . Despite of that, using Deep Learning for sentiment analysis in Twitter has not yet shown a big improvement in comparison to feature extraction, the fifth and sixth systems BIBREF5 in 2016 which were built upon feature extraction process were only (3 and 3.5% respectively) less than the first system. But We think that Deep Learning is a promising direction in sentiment analysis. Therefore, we proposed to use convolutional networks for Twitter polarity classification. Our proposed system consists of a convolutional layer followed by fully connected layer and a softmax on top. This is inspired by kimconvolutional2014, we just added a fully connected layer. This architecture gives a good performance but it could be improved. Regarding the best system in 2016 BIBREF6 , it uses different word embeddings for initialisation then it combines the predictions of different nets using a meta-classifier, Word2vec and Glove have been used to vary the tweet representation. In our work, we propose to vary the neural network weights instead of tweet representation which can get the same effect of varying the word embeddings, therefore we vary the initial weights of the network to produce ten different nets, a voting system over the these ten voters will decide the sentiment label for a tweet. The remaining of this paper is organized as follows: Section 2 describes the system architecture, Section 3 presents our experiments and results and Section 4 is devoted for the conclusion.

Question: how many sentiment labels do they explore?
Answer: 3