At the heart of the data warehouse is the database. It is crucial to build the data warehouse on a high-performance database engine that will meet both current and future needs of the organization. Relational database management systems (RDBMS) are the most common reservoirs for the large volumes of information stored in data warehouses. Increasingly, relational systems are being augmented with multidimensional OLAP (MOLAP) servers that provide enhanced navigational capabilities and increased performance for complex queries. Also important are facilities for replicating databases reliably from central data warehouses to dependent data marts, and ensuring consistency between mirrored data marts distributed geographically.