Dimensions can contain references to other dimensions. Although these relationships can be modeled with outrigger dimensions, in some cases, the existence of a foreign key to the outrigger dimension in the base dimension can result in explosive growth of the base dimension because type 2 changes in the outrigger force corresponding type 2 processing in the base dimension. This explosive growth can often be avoided if you demote the correlation between dimensions by placing the foreign key of the outrigger in the fact table rather than in the base dimension. This means the correlation between the dimensions can be discovered only by traversing the fact table, but this may be acceptable, especially if the fact table is a periodic snapshot where all the keys for all the dimensions are guaranteed to be present for each reporting period.