Hetero-Homogeneous Hierarchies in Data Warehouses

Data Warehouses facilitate multi-dimensional analysis of data from various data sources. While the original data sources are often heterogeneous, current modeling and implementation techniques discard and, thus, cannot exploit these heterogeneities. In this paper we introduce Hetero-Homogeneous Hierarchies to model dimension hierarchies and cubes with inherent heterogeneities. Hetero-homogeneous hierarchies are hierarchies that are heterogeneous in regard to the schema of sub-hierarchies and homogeneous in regard to a minimal common schema shared by all sub-hierarchies. Sub-dimension-hierarchies can be specialized to contain additional levels and additional non-dimensional attributes. Sub-cubes can be specialized towards additional measures, more fine-grained facts, and differing units of measure. We show how scale differences and conflicts due to multi-dimensional inheritance can be avoided and solved. We provide a formal definition of our approach together with a query/cube algebra.