Dealing with Dimensions in Data Warehousing
Jaroslav Pokorný · Kluwer Academic Publishers eBooks · 2005
In this paper we present a new approach to the notion of dimension in data warehouses modelling. Based on a four-level architecture, a model of dimension and fact tables is considered. A variant of the constellation schema with explicit dimension hierarchies is studied in detail. A dimension hierarchy H is extended to contain ISA-hierarchies built as specializations of H members. Derived tables can be created by restrictions on attributes of H members. Some graph-theoretic properties of H are formulated and the correctness of derived table definitions is discussed. As a consequence, the relationship of a correct derivation of tables to so-called join trees known from relational theory is shown. The same principles of correctness testing are applicable on specifications of views over dimensions as well as on queries over DWs designed as constellations with explicit dimension hierarchies.