A method of categorizing objects in which there can be multiple categories of objects and each object can belong to more than one category is described. The method defines a set of categories in which at least one category is dependent on another category and then organizes the categories in a hierarchy that embodies any dependencies among them. Each object is assigned to one or more categories in the set. A set of labels corresponding to all combinations of any number of the categories is defined, wherein if an object is relevant to several categories, the object must be assigned the label corresponding to the subset of all relevant categories. Once the new labels are defined, the multi-category, multi-label problem has been reduced to a multi-category, single-label problem, and the categorization task is reduced down to choosing the single best label set for an object.