Wednesday, 9 April 2014

What is Dimension & Types of Dimensions with Examples

Dimension Table
                      It is the Master Table of Cube. It contains textual information more and more. Generally
A Specific business information (or) A particular task information is stored in this table. It is a collection
Of Hierarchies, Categories and logics. This can be used for a user to traverse in hierarchical nodes.

Types of Dimensions

Confirmed Dimension
The Dimension which is shared by two or more Fact tables (if it is used in multiple projects) is called as confirmed Dimension.
(Or)
The Dimension which is created only once and it is used in many schemas then it is called Confirmed Dimension.

Example: Customer Dimension can be used across the saving & current Fact Tables in Banking Environment.


Role Playing Dimension
A database Dimension that acts as multiple dimensions with in a cube is called as Role Playing Dimension. From the same table if we have multiple foreign keys in fact tables then the table acts differently for each key attribute.

Example:
Time Dimension is one of the best Example of Role playing Dimension, you can have one Time Dimension called Date and then you can add ShipDate, DueDate and OrderDate as Cube Dimensions.


Junk Dimension

It is a group of flags which gives true or false, yes or no, type of information. The attributes in the junk dimension do not belongs to the fact table. It contains a Unique key for all possible combinations of flags and use that unique key in the fact table.
This is not relegated to any Data warehouse schema and is used only for reference.

Example:



Degenerated Dimension
It is a Dimension which is derived from fact tables and does not have its Entry in Dimension Tables.

Example:


In above table contains Fact Internet Sales information directly taken from OLTP Database. We will create dimension table depends on Fact Table like this



Note: IF number of Rows in Fact Table = Number of Rows in Dimension Table (That time De-Generated Dimension is not possible)

Slowly Changing Dimension
                   * link as shown below *
        Slowly changing dimension & scd-types URL Link

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