Star Model && Snowflake model

Star Modeis a multidimensional data relationship that consists of a fact table (Fact table) and a

The Group dimension table (Dimension table) is composed. Each dimension table has one dimension as the primary key, and all of these dimension's primary keys are grouped into the primary keys of the fact table. The non-primary key properties of the fact table are called facts (Fact), which are typically numeric or other data that can be computed, while the dimensions are mostly data of type, time, etc. By organizing the data in this way we can sum the facts (summary), average (average), count (count), percent (percent), or even 20~80 analysis according to the different dimensions (some or all of the primary key of the fact table). This allows you to analyze business topics from a number of different angles.

The snowflake model is called a snowflake model when one or more of the dimension tables are connected to the fact table without direct connection to the fact table, and the diagram is connected to the facts tables as multiple snowflakes. The snowflake model is an extension of the star model. When one or more dimension tables are not directly connected to the fact table, but are connected to the fact table through other dimension tables, their diagrams are like multiple snowflakes connected together, so the snowflake model is called. The snowflake model is an extension of the star model. It is further hierarchical to the dimension table of the star model, the original dimension table may be extended to small fact table, forming some local "level" area, these decomposed tables are connected to the primary dimension table instead of the fact table. Compared with the star model, the snowflake model is characterized by close to the business, less data redundancy, but due to the increase of the table connection, the efficiency relative to the star model to lower.

The snowflake model makes use of normalized data , which means that the data is organized inside the database to eliminate redundancy, so it can effectively reduce the amount of data. by referential integrity, the business levels and dimensions are stored in the data model

Star pattern a model that uses relational databases to implement multidimensional analysis space, called star mode.

Snowflake mode, for whatever reason, the star pattern evolves into snowflake mode when the dimension of the star pattern needs to be normalized.

Organize the Clear blog:http://yangjinyu.dream.blog.163.com/blog/static/115148886201322041022841/