What is the difference between MOLAP, ROLAP, and HOLAP?
A. Remember that a cube is pre-calculated summaries (aggregates) of your data mart data. MOLAP, ROLAP, and HOLAP are different methods of storing these aggregates on disk. Here is a summary of their major features: • MOLAP (Multidimensional OLAP)—Stores the aggregates and the base-level data in your data mart into a number of proprietary files. While this requires a bit more hard disk space, it is the fastest type of cube accessibility and it greatly reduces the strain on your data mart. • ROLAP (Relational OLAP)—Stores the aggregates in your data mart as tables alongside your base-level data. While this minimizes the hard disk space needed, it is the slowest type of cube access. • HOLAP (Hybrid OLAP)—A compromise between MOLAP and ROLAP. The aggregates are stored in a MOLAP file, while the base-level detail is kept in the data mart. This provides excellent performance while browsing aggregates, but is slow when a user “drills down” to base-level detail. Usually, MOLAP is the best choi
