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Week 2 - Data Warehouse & OLAP (Difference between Data Warehouse &…
Week 2 - Data Warehouse & OLAP
Difference between Data Warehouse & Operational Database
OLTP Vs OLAP
What is a data warehouse?
Characteristics of DW data
Data Warehousing Process (ETL)
Types of Data Warehouses
Data Marts etc.
Representation of data in data warehouse
Star Schema
Snowflake Schema
Normalised & FK in fact table point to the lowest level of hierarchy (more detailed)
Constellation Schema
More than one fact table
Note: Measure = calculations can be made e.g. prices, quantity, Dimension = categorise measures e.g. people, products, place & time
Fact table = measures + FK for each dimension
3 types of facts
Addictive
can be added
Semi-Addictive
can be added from some dimensions
Non-addictive
cannot be combined to get total e.g. ratios/%
Types of Dimensions (3 types of SCD)
Type 1
Does not track changes
overwrites previous = inaccurate analysis
Type 2
Track changes, track history
Type 3
Do not track entire history of dimension
only current & original state
OLAP Operations
Slice
Dice
Drill Down
More detailed
Roll up
More summarised
Steps in Designing DW /Data Mart