EDH: A Powerful method for the modeling of Irregular Dimensions

Pre-aggregation is one of the most effective techniques in OLAP to ensure quick responses to user queries in data warehouses. Partial pre-aggregation is used widely, and the technique usually requires that the hierarchies of a dimension are onto, covering and self-onto. However, in real-world applications, many irregular dimensions do not meet the requirements. To solve the problem, in this paper, we propose a new dimension model to support the modeling of irregular dimensions based on extended directed Hasse graph. The model can express various relationships among dimension levels and different relationships among elements in the domain of a dimension. The model can also avoid aggregation loops in a dimension and ensure correct aggregation paths in the dimension by controlling the directions of paths and disallowing isolated nodes in EDH graphs. Thus, it can support both regular and irregular dimensions.