... computational model because of the difficulty of determining the unit of an opinion. In general, researchers study opinion at three different lev-els: word level, sentence level, and document level. ... a combination of two methods. The first method derived a list of opinion-bearing words from a large news corpus by separating opinion articles such as letters or editorials from news articles ... specific and tangible features. Also, there are somewhat a fixed set of features of a specific type of product, for exam-ple, ease of use, durability, battery life, photo quality, and shutter lag...