I. Introduction
Internet expansion allows companies to improve their selling capabilities on a world-wide visibility and also enables potential buyers to compare and buy products in a much faster and cheaper way than visiting a store. Studies revealed that when it comes to decision making, customers prefer to gather information online than from in-store due to the richness of the information available to them on the Internet [1], [2], [3]. Many major businesses and online traders enable customers to provide online reviews about products that they have purchased. Customers usually provide a written review accompanied by a numerical rating representing their overall satisfaction level for the transaction. Companies use customer feedback to provide potential buyers with information about the quality and user satisfaction for a given product or service. For this reason, reviews have an important impact on businesses performance and they can affect the performance of a company in terms of sales volume and market shares. Opinion mining of customer review ratings is becoming an important task for e-commerce, because companies can extract customer opinions from reviews about specific products in order to determine customer satisfaction based on the degree of positivity of the reviews, and predict demand of current and future products. The data found between the textual reviews and their numerical ratings can be uncertain, and the size of database storing customer reviews could be too big to be accurately analysed by conventional machine learning algorithms, such as neural networks. In order to deal with such large and noisy information, data mining techniques should be efficiently applied to the data in order to reduce the size of the data. As a consequence, only the most important features should be extracted from the textual reviews and used by the system to automatically compute a corresponding rating. The reduced representation of the data is a more suitable and accurate than raw information directly provided by customers after their purchases, and it can be used for performing future marketing activities. As shown in Section II, several intelligent systems have been designed to face this significant challenge, but none of them addressed the rating prediction issue by considering all of the involved difficulties: the dimensionality of data and system accuracy.