According to
Ralph Kimball
Ralph Kimball (born July 18, 1944) is an author on the subject of data warehousing and business intelligence. He is one of the original architects of data warehousing and is known for long-term convictions that data warehouses must be designed to b ...
,
in a
data warehouse
In computing, a data warehouse (DW or DWH), also known as an enterprise data warehouse (EDW), is a system used for reporting and data analysis and is considered a core component of business intelligence. DWs are central repositories of integra ...
, a degenerate dimension is a dimension key in the
fact table
In data warehousing, a fact table consists of the measurements, metrics or facts of a business process. It is located at the center of a star schema or a snowflake schema surrounded by dimension tables. Where multiple fact tables are used, thes ...
that does not have its own
dimension table
A dimension is a structure that categorizes facts and measures in order to enable users to answer business questions. Commonly used dimensions are people, products, place and time. (Note: People and time sometimes are not modeled as dimensions.) ...
, because all the interesting attributes have been placed in analytic dimensions. The term "degenerate dimension" was originated by
Ralph Kimball
Ralph Kimball (born July 18, 1944) is an author on the subject of data warehousing and business intelligence. He is one of the original architects of data warehousing and is known for long-term convictions that data warehouses must be designed to b ...
.
As Bob Becker says:
Other uses of the term
Although most writers and practitioners use the term degenerate dimension correctly, it is very easy to find misleading definitions in online and printed sources. For example, the Oracle FAQ defines a degenerate dimension as a "data dimension that is stored in the fact table rather than a separate dimension table. This eliminates the need to join to a dimension table. You can use the data in the degenerate dimension to limit or 'slice and dice' your fact table measures."
This common interpretation implies that it is good dimensional modeling practice to place dimension attributes in the fact table, as long as you call them a degenerate dimension. This is not the case; the concept of degenerate dimension was developed by Kimball to support a specific, well-defined exception to the otherwise ironclad rule that dimension attributes are always pulled out into dimension tables.
See also
*
data warehouse
In computing, a data warehouse (DW or DWH), also known as an enterprise data warehouse (EDW), is a system used for reporting and data analysis and is considered a core component of business intelligence. DWs are central repositories of integra ...
*
dimension table
A dimension is a structure that categorizes facts and measures in order to enable users to answer business questions. Commonly used dimensions are people, products, place and time. (Note: People and time sometimes are not modeled as dimensions.) ...
*
fact table
In data warehousing, a fact table consists of the measurements, metrics or facts of a business process. It is located at the center of a star schema or a snowflake schema surrounded by dimension tables. Where multiple fact tables are used, thes ...
*
measure (data warehouse)
Notes
Bibliography
*
Kimball, Ralph et al. (1998); ''The Data Warehouse Lifecycle Toolkit'', p17. Pub. Wiley. .
*
Kimball, Ralph (1996); ''The Data Warehouse Toolkit'', p. 100. Pub. Wiley. .
External links
*
{{Data warehouse
Data warehousing
Metadata