ROLAP architecture provides a multi-dimensional view of the data to the user, but stores the data in the relational database format. This architecture goes with the logic that relational storage of data can give much higher level of scalability, can absorb as many dimensions etc. as needed, and can provide faster response time due to indexing and other features.

This logic becomes more valid, when you are storing the data in RDBMS in a dimension partially normalized model and not in a traditional E-R normalized model.
The way a ROLAP works is that it stays stored in the data warehouse, and unlike MOLAP, there is no database as such in a ROLAP server. ROLAP server contains the analytics objects, which create dynamic aggregation of the RDBMS data in Data Warehouse, and present it to the user.
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