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1.Star model Star Model: is a multi-dimensional data relationship that consists of a Fact Table and a set of Dimension Tables. Each Dimension Table has a dimension as its primary key, and the primary keys of all these dimensions are combined to form the primary key of the Fact Table. The non-primary key attributes of a Fact Table are called Facts, and they are generally numeric values or other data that can be computed. As shown in the following figure: 2.Snowflake model Snowflake model: When one or more dimensional tables are not directly connected to the fact table, but are connected to the fact table through other dimensional tables, the illustration is like multiple snowflakes connected together, so it is called snowflake model. The snowflake model is an extension of the star model, which further hierarchises the dimensional tables of the star model, and the original dimensional tables may be extended into small fact tables to form some local "hierarchical" regions, and these decomposed tables are connected to the main dimensional table instead of the fact table. 3.Multi-dimensional table multi-fact table model 4.Multi-fact table model | 
