Data Mining Interview Questions and Answers

 

What are the primary ways to store data in OLAP?

"There are primary three ways in which we store information in OLAP:



1. MOLAP:

Multidimensional OLAP (MOLAP)


stores dimension
and fact data in a persistent data



store using compressed indexes. Aggregates are stored to facilitate fast data access.



MOLAP query engines are usually proprietary and optimized for the storage format
used



by the MOLAP data store. MOLAP offers faster query processing than ROLAP and



usually requires less storage. However, it doesn’t scale as well and requires a
separate



database for storage.



2. ROLAP:

Relational OLAP (ROLAP)


stores aggregates in
relational database tables. ROLAP use



of the relational databases allows it to take advantage of existing database resources,



plus it allows ROLAP applications to scale well. However, ROLAP’s use of tables
to



store aggregates usually requires more disk storage than MOLAP, and it is generally
not



as fast.



3. HOLAP:

As its name suggests,


Hybrid OLAP (HOLAP)



is a cross between MOLAP and ROLAP.



Like ROLAP, HOLAP leaves the primary data stored in the source database. Like MOLAP,



HOLAP stores aggregates in a persistent data store that’s separate from the primary



relational database. This mix allows HOLAP to offer the advantages of both MOLAP



and ROLAP. However, unlike MOLAP and ROLAP, which follow well-defined standards,



HOLAP has no uniform implementation. "

Posted by:Richards