Chapter 12

Question 1

Why we need ROLAP

Answer 1

We need relational OLAP because when numbers of dimensions increases then cube size increases in MOLAP and a time comes when MOLAP could not fit in main memory so then we need ROLAP. In short it is for scalability.

Question 2

What is aggregate awareness

Answer 2

It is a concept that system should aware of available aggregates and use them when required. If available aggregate does not fit in requirement then use them to make new higher level aggregates to make query

Question 3

What is star schema

Answer 3

Star schema designs usually used to support ROLAP querying. The star schema is the simplest style of data mart schema and is the approach most widely used to develop data warehouses and dimensional data marts. The star schema consists of one or more fact tables referencing any number of dimension tables.

Question 4

What is fact table

Answer 4

The fact table is a way of visualizing as a un-rolled cube

Question 5

Cube is what dimensional structure

Answer 5

1

Question 6

What is cube

Answer 6

Cube is a logical entity containing values of a certain fact

Question 7

What is cube clause

Answer 7

This is a clause in SQL in which we can specify number of columns and an efficient replacement of GROUP By clause

Question 8

What are ROLAP issues

Answer 8

• Maintenance
• Non standard hierarchy of dimension
• Non standard convention
• Explosion to storage space requirement
• Aggregation pit-falls

Question 9

What is Non standard hierarchy of dimension in ROLAP

Answer 9

Dimensions are not always simple hierarchies