hybrid OLAP (HOLAP)
There are different techniques for storing multidimensional data structures, so-called OLAP cubes: Multidimensional OLAP( MOLAP), Relational OLAP( ROLAP) and Hybrid OLAP (HOLAP). In HOLAP, hybrid OLAP, the data is stored partly in the database server and partly in the OLAP server.
As in Relational OLAP (ROLAP), in Hybrid OLAP (HOLAP) the detailed data is stored in a relational database. The aggregations, on the other hand, are stored in a multidimensional structure on the OLAP cube, as in MOLAP.
For the detail data, the tables that are filled by the ETL process (extract/transform/load) are usually used. This approach allows both advantages of MOLAP and ROLAP to be used together. The main disadvantage is that the data of the OLAP cube is stored in different locations.
Access to the underlying relational database is necessary only when accessing detailed data. The graphic shows where the data is located in the different storage techniques.
The three storage techniques have different characteristics:
HOLAP is therefore particularly suitable for multidimensional data with a large to very large volume, with many aggregation levels, e.g. for very extensive sales data of a multinational company.