In data warehousing, a dimension table is one of the set of companion tables to a fact table. A data warehouse is a Repository of an organization's electronically stored data In Data warehousing, a fact table consists of the measurements metrics or Facts of a Business process.
The fact table contains business facts or measures and foreign keys which refer to candidate keys (normally primary keys) in the dimension tables. In the context of Relational databases a foreign key is a referential constraint between two tables In the Relational model, a candidate key of a Relvar (relation variable is a Set of attributes of that relvar such that at all times it holds In Relational database design a unique key or primary key is a Candidate key to uniquely identify each row in a table.
The dimension tables contain attributes (or fields) used to constrain and group data when performing data warehousing queries. Debt AIDS Trade in Africa (or DATA) is a Multinational non-government organization founded in January 2002 in London by U2 's A data warehouse is a Repository of an organization's electronically stored data
Over time, the attributes of a given row in a dimension table may change. For example, the shipping address for a company may change. Kimball refers to this phenomenon as Slowly Changing Dimensions. Ralph Kimball is an author on the subject of Data warehousing and Business intelligence. Strategies for dealing with this kind of change are divided into three categories:
- Type One - Simply overwrite the old value(s).
- Type Two - Add a new row containing the new value(s), and distinguish between the rows using Tuple-versioning techniques. Tuple-versioning (also called point-in-time) is a mechanism used in a Relational database management system to store past states of a Relation.
- Type Three - Add a new attribute to the existing row.
See also
References
- Kimball, Ralph et al (1998); The Data Warehouse Lifecycle Toolkit, p17. A data warehouse is a Repository of an organization's electronically stored data For other senses of dimension see Dimension (disambiguation. In a Data warehouse, a dimension is a Data element that categorizes Ralph Kimball is an author on the subject of Data warehousing and Business intelligence. Year 1998 ( MCMXCVIII) was a Common year starting on Thursday (link will display full 1998 Gregorian calendar) Pub. Wiley. ISBN 0-471-25547-5.
- Kimball, Ralph (1996); The Data Warehouse Toolkit, p100. Ralph Kimball is an author on the subject of Data warehousing and Business intelligence. Year 1996 ( MCMXCVI) was a Leap year starting on Monday (link will display full 1996 Gregorian calendar) Pub. Wiley. ISBN 0-471-15337-0.
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