MOLAP and ROLAP

ROLAP

The Relational OLAP servers are placed between relational back-end server and client front-end tools. To store and manage warehouse data the Relational OLAP use relational or extended-relational DBMS. ROLAP includes the following. 

 

• Implementation of aggregation navigation logic.
• Optimization for each DBMS back end.
• Additional tools and services.

Note: The ROLAP servers are highly scalable.

Points to remember

The ROLAP tools need to analyze large volume of data across multiple dimensions.

The ROLAP tools need to store and analyze highly volatile and changeable data.

Relational OLAP Architecture

The ROLAP includes the following.

• Database Server
• ROLAP Server
• Front end tool 

Advantages

The ROLAP servers are highly scalable.

1. They can be easily used with the existing RDBMS.
2. Data Can be stored efficiently since no zero facts can be stored.
3. ROLAP tools do not use pre-calculated data cubes.
4. DSS server of microstrategy adopts the ROLAP approach.

Disadvantages

• Poor query performance.
• Some limitations of scalability depending on the technology architecture that is utilized.

 Multidimensional OLAP

Multidimensional OLAP (MOLAP) uses the array-based multidimensional storage engines for multidimensional views of data. With multidimensional data stores, the storage utilization may be low if the data set is sparse. Therefore many MOLAP Server uses the two level of data storage representation to handle dense and sparse data sets.

 

Points to remember:

MOLAP tools need to process information with consistent response time regardless of level of summarizing or calculations selected.

• The MOLAP tools need to avoid many of the complexities of creating a relational database to store data for analysis.
• The MOLAP tools need fastest possible performance.
• MOLAP Server adopts two level of storage representation to handle dense and sparse data sets.
• Denser subcubes are identified and stored as array structure.
• Sparse subcubes employ compression technology.

MOLAP Architecture

MOLAP includes the following components.

• Database server
• MOLAP server
• Front end tool

Advantages

Here is the list of advantages of Multidimensional OLAP

• MOLAP allows fastest indexing to the precomputed summarized data.
• Helps the user who is connected to a network and need to analyze larger, less defined data.
• Easier to use therefore MOLAP is best suitable for inexperienced user.

Disadvantages

MOLAP are not capable of containing detailed data.

The storage utilization may be low if the data set is sparse.

SN	MOLAP	ROLAP
1	The information retrieval is fast.	Information retrieval is comparatively slow.
2	It uses the sparse array to store the data sets.	It uses relational table.
3	MOLAP is best suited for inexperienced users since it is very easy to use.	ROLAP is best suited for experienced users.
4	The separate database for data cube.	It may not require space other than available in Data warehouse.
5	DBMS facility is weak.	DBMS facility is strong.