ROLAP means Relational OnLine Analytical Processing
The underlying data in this model is stored in relational databases.
Since the data is stored in relational databases this model gives the appearance of traditional OLAP’s slicing and dicing functionality.
MOLAP means Multidimensional OnLine Analytical Processing
This is the traditional mode in OLAP analysis. In MOLAP data is stored in form of multidimensional cubes and not in relational databases.
ROLAP
Advatages -
The advantages of this model is it can handle a large amount of data and can leverage all the functionalities of the relational database.
Disadvantages -
The disadvantages are that the performance is slow and each ROLAP report is an SQL query with all the limitations of the genre. It is also limited by SQL functionalities
ROLAP vendors have tried to mitigate this problem by building into the tool out-of-the-box complex functions as well as providing the users with an ability to define their own functions.
MOLAP
Advantages -
The advantages of this mode is that it provides excellent query performance and the cubes are built for fast data retrieval. All calculations are pre-generated when the cube is created and can be easily applied while querying data.
Disadvantages -
The disadvantages of this model are that it can handle only a limited amount of data. Since all calculations have been pre-built when the cube was created, the cube cannot be derived from a large volume of data. This deficiency can be bypassed by including only summary level calculations while constructing the cube. This model also requires huge additional investment as cube technology is proprietary and the knowledge base may not exist in the organization.
