Molap and Rolap

What is Molap and Rolap and whats the difference between these tw开发者_运维问答o ?

MOLAP = Multidimensional Online Analytical Processing
ROLAP = Relational Online Analytical Processing

Essentially with ROLAP, the data is stored in a relational database, whereby with MOLAP, i.e. the traditional OLAP model, this is stored in multidimentional "cubes". Cubes are a multidimensional structure similar to the star schema in an RDBMS, but where the management of the storage is highly optimized to deal with such a structure.

At the risk of adding to the alphabet soup, another model is HOLAP, for Hybrid OLAP, which attempts to provide the best of traditional MOLAP with the benefits of "Relational" in ROLAP.

MOLAP's main advantage is its excellent query performance and fast data retrieval. Its main disadvantage is that is may be limited in the amount amount of data it can handle. Another disadvantage is the use of proprietary engines.

ROLAP's performance is slower, but it also it is less limited in term of the number of dimensions etc.

These are terms associated with Datawarehousing. ROLAP is relational OLAP.