Presented By:Abhishek Das (V1062)Neha Topno (V1113)Abhinav Shukla (V1061)Praveen SinghBijay

A snowflake schema is a logical arrangement of tables in a multidimensional database used in data warehousing

The snowflake schema is represented by centralized fact tables

However, dimensions are normalized into multiple related tables

The star schema is the simplest data warehouse schema

It is a denormalised model. No need to use complicated joins

A star schema can have any number of dimension tables

Fact Table Dimension Table

•A fact table is a table in a star or snowflake schema that stores facts that measure the business, such as sales, cost of goods, or profit•Fact tables also contain foreign keys to the dimension tables. These foreign keys relate each row of data in the fact table to its corresponding dimensions and levels

•A dimension table is a table in a star or snowflake schema that stores attributes that describe aspects of a dimension•For example, a time table stores the various aspects of time such as year, quarter, month, and day. A foreign key of a fact table references the primary key in a dimension table in a many-to-one relationship

Advantages Disadvantages

·  In some cases may improve performance because smaller tables are joined, ·  Is easier to maintain, ·  Increases flexibility

·  Increases the number of tables an end-user must work with, ·   Makes the queries much more difficult to create because more tables need to be joined

Advantages Disadvantages

•Reduced Joins, Faster Query Operation

•Writing queries becomes simpler as there are no complex joins in the ERD

•Work of end- user becomes easy because of less complexity

•Bigger table sizes because of large number of dimension tables

•Denormalized form of a snowflake schema

•Too many rows in Fact Table

· Fact Table and its contents:  metric attributes and the foreign keys necessary to join to the dimension tables, · Dimension Tables and their contents:  reference attributes and metric attributes.  The dimension tables are normalized, · The lines that link the Dimension Tables to the Fact Table, · The lines that link the Dimension Tables to more Dimension Tables.

Snowflake Schema

· Fact Table and its contents:  metric attributes and the foreign keys necessary to join to the dimension tables, · Dimension Tables and their contents:  reference attributes and metric attributes.  The dimension tables are normalized, · The lines that link the Dimension Tables to the Fact Table, 

Starflake Schema

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