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How many types of dimension tables available in data warehouse?
Data warehouse have six types of dimension table.
1. Conformed Dimensions
when a particular dimension is connected to one or more fact tables. ex) time dimension
2. Parent-child Dimensions
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A parent-child dimension is distinguished by the fact that it contains a hierarchy based on a recursive relationship.
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when a particular dimension points to its own surrogate key to show an unary relationship.
3. Role Playing Dimensions
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when a particular dimension plays different roles in the same fact table. ex) dim_time and orderDateKey, shippedDateKey...usually a time dimension table.
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Role-playing dimensions conserve storage space, save processing time, and improve database manageability .
4. Slowly Changing Dimensions:
A dimension table that have data that changes slowly that occur by inserting and updating of records.
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Type 0: columns where changes are not allowed - no change ex) DOB, SSNm
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Type 1: columns where its values can be replaced without adding its new row - replacement
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Type 2: for any change for the value in a column, a new record it will be added - historical data. Previous values are saved in records marked as outdated. For even a single type 2 column, startDate, EndDate, and status are needed.
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Type 3: advanced version of type 2 where you can set up the upper limit of history which drops the oldest record when the limit has been reached with the help of outside SQL implementation.
Type 0 ~ 2 are implemented on the column level.
5. Degenerated Dimensions:
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a particular dimension that has an one-to-one relationship between itself and the fact table.
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When a particular Dimension table grows at the same rate as a fact table, the actual dimension can be removed and the dimensions from the dimension table can be inserted into the actual fact table.
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You can see this mostly when the granularity level of the the facts are per transaction.
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Example: The dimension salesorderdate (or other dimensions in DimSalesOrder would grow everytime a sale is made therefore the dimension (attributes) would be moved into the fact table.
6. Junk Dimensions: holds all miscellaneous attributes that may or may not necessarily belong to any other dimensions. It could be yes/no, flags, or long open-ended text data.
Thank You
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Brijesh Kumar
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I have more then 6 years Experience in Microsoft Technologies - SQL Server Database, ETL
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