OLAP tools enable interactive analysis of multidimensional data from multiple perspectives. There are three main types of OLAP tools: ROLAP, MOLAP, and HOLAP. ROLAP uses relational databases and SQL queries, while MOLAP pre-computes and stores aggregated data in multidimensional arrays for fast querying. HOLAP is a hybrid that stores some data in ROLAP and some in MOLAP to optimize both query performance and cube processing time.

1. Online Analytical
Processing
(OLAP) Tools
Anurag A. Kulkarni

2. OLAP Tools
• OLAP tools enable users to analyse multidimensional data
interactively from multiple perspectives.
• Types of Tools
• Relational Online Analytical Processing (ROLAP)
• Multidimensional Online Analytical Processing (MOLAP)
• Hybrid Online Analytical Processing (HOLAP)

3. Relational Online Analytical Processing
(ROLAP)
• ROLAP tools access the data in a “Relational Database” and
generate “SQL queries” to calculate information at the
appropriate level when an end user requests it.
• ROLAP does not require the pre-computation and storage of
information.
• With ROLAP, it is possible to create additional database tables

4. Advantages of ROLAP
• ROLAP is considered to be more scalable in handling large data
volumes (Dimensions and Cardinality i.e. millions of members)
• Load time is much shorter than the MOLAP.
• Data stored in the R-database can be accessed by any other
SQL reporting tool.
• ROLAP tools are better at handling textual data.
• By decoupling the data storage from the multi-dimensional
model, it is possible to successfully model data.

5. Disadvantages of ROLAP
• ROLAP Tools have slower performances than MOLAP. (except
loading time)
• Since ROLAP tools rely on SQL for all of the computations,
they are not suitable when the model is heavy on calculations
which don't translate well into SQL.
• There are several techniques which are employed by MOLAP
are not available with ROLAP (e.g. hierarchical indexing).
• ROLAP doesn't support ETL i.e. Extract Transform and Load, so
additional development time and code is required.

6. Multidimensional Online Analytical
Processing (MOLAP)
• MOLAP is a alternative to ROLAP technology.
• MOLAP Tools allow analysis of data through the use of
multidimensional data model.
• MOLAP requires “pre-computation” and “storage” of
information in cube.
• Operations on MOLAP is known as “processing”.
• MOLAP solutions store these data in multistorage array.

7. Advantages of MOLAP
• Fast Query Performance due to optimized storage due to
indexing and caching.
• Smaller size of data as compared to relational database.
• Automated computation of higher level of aggregates of the
data.
• It is very compact for low dimension data sets.
• Array models provide natural indexing.
• Effective data extraction achieved through the pre-structuring
of aggregated data.

8. Disadvantages of MOLAP
• MOLAP Solutions the processing step (data load) can be quite
lengthy, especially on large data volumes.
• MOLAP tools traditionally have difficulty querying models
with dimensions with very high cardinality.
• MOLAP products have difficulty updating and querying models
with more than ten dimensions, this limit differs depending on
the complexity and cardinality of the dimensions.
• Some MOLAP methodologies introduce data redundancy.

9. Hybrid Online Analytical Processing
(HOLAP)
• HOLAP is the combination of ROLAP and MOLAP.
• HOLAP allows the storing part of data in a MOLAP store and
other part of the data in the ROLAP store.
• Its supports two partitioning…
• Vertical Partitioning : In this mode HOLAP stores aggregations
in MOLAP for fast query performance, and detailed data in
ROLAP to optimize time of cube processing.
• Horizontal Partitioning : In this mode HOLAP stores some slice
of data, usually the more recent one in MOLAP for fast query
performance, and older data in ROLAP.