Schemas and its types :
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:
- Star schema
- Snow flake schema
- Galaxy schema (or)integrated schema (or) constellation 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:
- A dimensional table contains detail information (or) descriptive information
- Dimensions are used to describe the facts.
- 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.
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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
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