1. A method of storing data in a multi-dimensional database, such that values at two different levels of a hierarchically structured dimension are recovered from stored data, said method comprising: providing the multi-dimensional database to store data at a lowest level of said hierarchically structured dimension, as executed by a processing unit of a computer; storing at least one value in at least one category within the lowest level of said hierarchically structured dimension; identifying a desired value from a level that is higher than the lowest level of said hierarchically structured dimension in the multi-dimensional database; calculating, in the processing unit of the computer, a second value at said level that is higher than the lowest level of said hierarchically structured dimension in the multi-dimensional database, based upon an aggregation of said at least one value over said at least one category within the lowest level of said hierarchically structured dimension; determining a difference between the desired value and the second value; creating a dummy category including a new category at the lowest level of said hierarchically structured dimension; storing the difference in the new category at the lowest level of said hierarchically structured dimension; and aggregating the values at the lowest level of said hierarchically structured dimension, such that the desired value at an upper level is obtained.