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Multidimensional Data Model

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A MULTIDIMENSIONAL DATA MODEL
Data warehouses and OLAP tools are based on a multidimensional data model. This model views data in the form of a data cube.
FROM TABLES TO DATA CUBES
What is a data cube?
A data cube allows data to be modeled and viewed in multiple dimensions. It is defined by dimensions and facts.
In general terms, dimensions are the perspectives or entities with respect to which an organization wants to keep records. Each dimension may have a table associated with it, called a dimension table, which further describes the dimension.
Facts are numerical measures. The fact table contains the names of the facts, or measures, as well as keys to each of the related dimension tables.
Example:
2-D representation, the sales …show more content…

Fact constellation:
Sophisticated applications may require multiple fact tables to share dimension tables. This kind of schema can be viewed as a collection of stars, and hence is called a galaxy schema or a fact constellation.

Fact constellation schema of a data warehouse for sales and shipping

This schema species two fact tables, sales and shipping. The sales table definition is identical to that of the star schema. A fact constellation schema allows dimension tables to be shared between fact tables.
In data warehousing, there is a distinction between a data warehouse and a data mart. A data warehouse collects information about subjects that span the entire organization, such as customers, items, sales, assets, and personnel, and thus its scope is enterprise-wide. For data warehouses, the fact constellation schema are commonly used since it can model multiple, interrelated subjects.
A data mart, on the other hand, is a department subset of the data warehouse that focuses on selected subjects, and thus its scope is department-wide. For data marts, the star or snowflake schemas are popular since each are geared towards modeling single subjects.
Examples for defining star, snowflake, and fact constellation schemas
In DMQL, The following are the syntax to define the Star, Snowflake, and Fact constellation Schemas:

MEASURES:

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