1. A computer-implemented method for forecasting demand for order configurations, comprising: receiving, using a processor, data associated with one or more products and said order configurations; defining a set of subproducts arranged in a hierarchy wherein each level of the hierarchy includes one or more option classes and wherein each of said classes includes one or more options represented as a set of nodes; expressing attach rates associated with n options as a set of n positive numbers whose sum is one, an attach rate representing a proportion of a product for which an option is requested; transforming said attach rates as a random vector in n−1 dimensional Euclidean space; modeling a distribution of the transformed attach rates as a distribution family specified by a location vector and a dispersion matrix of forecast errors, and reducing number of nonzero elements of the dispersion matrix by identifying categories of dependence (a) between options in the same class at a single node of a hierarchy, (b) between options in different classes at a single node of the hierarchy, (c) between the same option at different nodes of the hierarchy, (d) between options in the same class at different nodes of the hierarchy, (e) between options from different classes at different nodes of the hierarchy, wherein the hierarchy represents the product and classes of options as nodes in a hierarchical representation wherein selected dispersion matrix elements for pairs of nodes in a category are constrained to be equal, and wherein if two option classes are determined to be independent, the dispersion matrix has entries that reflect independence between every pair of transformed attach rates that contains one member from each of the two option classes, and wherein the dispersion matrix elements for pairs of nodes that are reflected as independent are constrained to be zero; estimating a location vector of the distribution by computing point forecasts of the transformed attach rates; estimating, by the processor, a dispersion matrix of the distribution, the dispersion matrix describing variability of the forecast errors of the transformed attach rates; and transforming said location vector and said dispersion matrix to forecast attach rates.