Schemas and its types in Cognos

Schemas and its types :

Schema:

A schema is nothing but a collection of objects

• Designing a dWH is nothing but designing the schema
• A data ware house tables are contain dimensional tables and fact tables
• Database models follows dimensional modeling to design dWH schema
• Dimensional modeling is a process of creating dimensional tables and fact tables with proper relation

Types of schemas:

1. Star schema
2. Snow flake schema
3. Galaxy schema (or)integrated schema (or) constellation schema

STAR SCHEMA:

A star schema design is a data base design where the centrally located table is called fact table with surrounded by number of dimensional tables

• Since the database design looks like star, it is called star schema

Format of star schema:

Dimensional tables:

• A dimensional table contains detail information (or) descriptive information
• Dimensions are used to describe the facts.

Fact table: 

• A fact table contains all the key columns (PK, FK) and measures of the particular business organizations.
• Measures are also called as facts (or) KPI’s (key performance indications)
• fact should be a numeric but every numeric near not be a fact.

Sales schema

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Snow flake schema:

Difference between the schema and snow flake schema:

Star schema	Snow flake schema
It is de normalizedRetrieval up data is faster redundancy is there	it is normalizedRetrieval up data is slower due to more number of icons redundancy can be reduced

Integrated schema:

For indepth understanding Cognos Training click on

• Cognos Tutorials
• Introduction to IBM COGNOS
• Dimensions & OLAP Types in Cognos
• Reporting Studio in IBM Cognos
• Fitters and its types in Cognos