Thus, we assume that the consumer gives the overall opinion rating O r based on the weighted sum of his/her opinion o rk on each aspect a k :  To model the uncertainty of the importance weights ω r in each review, we assume ω r as a sample drawn from a Multivariate Gaussian Distribution, with µ as the mean vector and Σ as the covariance matrix, We further incorporate aspect frequency as a prior knowledge to define the distribution of µ and Σ.
the distribution of µ and Σ is defined based on its Kullback-Leibler (KL) divergence to a prior distribution with a mean vector µ 0 and an identity covariance matrix I in Eq.3.