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star schema
In computing, the Star Schema is the simplest style of data mart schema. The star schema consists of one or more fact tables referencing any number of dimension tables. The star schema is an important special case of the snowflake schema, and is more effective for handling simpler queries.〔(【引用サイトリンク】title=DWH Schemas )〕
The star schema gets its name from the physical model's〔C J Date, "An Introduction to Database Systems (Eighth Edition)", p. 708〕 resemblance to a star shape with a fact table at its center and the dimension tables surrounding it representing the star's points.
== Model ==
The star schema separates business process data into facts, which hold the measurable, quantitative data about a business, and dimensions which are descriptive attributes related to fact data. Examples of fact data include sales price, sale quantity, and time, distance, speed, and weight measurements. Related dimension attribute examples include product models, product colors, product sizes, geographic locations, and salesperson names.
A star schema that has many dimensions is sometimes called a ''centipede schema''.〔Ralph Kimball and Margy Ross, ''The Data Warehouse Toolkit: The Complete Guide to Dimensional Modeling (Second Edition)'', p. 393〕 Having dimensions of only a few attributes, while simpler to maintain, results in queries with many table joins and makes the star schema less easy to use.
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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