Arjun

• Nov 1st, 2006

 

This is Entity - Relation model which is used for normalising the data

sathishkumar_sundaram

 Profile Answers by sathishkumar_sundaram 

• Nov 6th, 2006

 

Hi,

E-R model is Entity Relation model used in Two dimesional Databases.For Example, SQL Server, or Oracle. A table is based on two dimensions.Rows and Columns.Generally, OLTP systems are based on two dimensions.

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But, if you see in Dimensional modeling, We have more than two dimensions.

A cube represents a three dimensionsional model. In a DW house, the data are stored in the form of summary of information. Also, these data can be easily retrived from a DB compared to a normal OLTP Database.

Lets assume, PROD, GEOG, TIME and MEAS are the four dimensions we have. A DW System have stored information with these four dimensions. If you want to know the sales of Lux (Prod), in North India (Geog), during (Oct 2006) for a measure value of Lux 75 grams (MEAS).

ie., FACT_TBL(PROD LUX, GEOG NORTH_INDIA, TIME OCT06, MEAS Units) would give rise to some quantity say, 75809 Units. This means, in north india this many units have been sold during the given period.

This you can verywell access with a normal OLTP system. But the problem is when the size of the data grows, your system will not tollerate the load. Your query performance will die down. Not just this alone, for many other advantages, we need DWH instead of a normal OLTP system.

Thanks - Sathish.