Data warehouses contain huge volumes of data. OLAP servers demand that decision support queries be answered in the order of seconds. Therefore, it is crucial for data warehouse systems to support highly efficient cube computation techniques, access methods, and query processing techniques. In this section, we present an overview of methods for the efficient implementation of data warehouse systems. Section 4.4.1 explores how to compute data cubes efficiently. Section 4.4.2 shows how OLAP data can be indexed, using either bitmap or join indices. Next, we study how OLAP queries are processed (Section 4.4.3). Finally, Section 4.4.4 presents various types of warehouse servers for OLAP processing.