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Data Warehouse (VI): Examples of the star schema

Data Warehouse (VI): Examples of the star schema. Developed by: Dr Eddie Ip Modified by: Dr Arif Ansari. Outline. Review of concept of grain Advanced concepts Slowly changing dimensions Snow flake schema Additivity of measures & other issues PC Manufacturer example Homework 1B.

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Data Warehouse (VI): Examples of the star schema

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  1. Data Warehouse (VI): Examples of the star schema Developed by: Dr Eddie Ip Modified by: Dr Arif Ansari

  2. Outline • Review of concept of grain • Advanced concepts • Slowly changing dimensions • Snow flake schema • Additivity of measures & other issues • PC Manufacturer example • Homework 1B

  3. Dimension Fact

  4. Grain • Level of detail of data • Important concept – defines what a fact really represents

  5. Slowly changing dimension • Dimension tables are relatively stable • Sometimes still need change • Change different from OLTP • E.g., customer address change • Types of change • Type 1 • Type 2 • Type 3

  6. Slowly changing dimensions • Type 1 • Simple update • Type 2 • Add new row to dimension table • E.g., new address, same customer • Type 3 • Add new column • E.g., new territory designation of sales force

  7. Snow-flake schema • Dimension tables further normalized • Number of attributes large (high cardinality) • Create tables for attributes within a dimension table

  8. Snow-flake schema • E.g. store dimension has district as attribute • District has district description, district manager, district HQ attributes • Alternative design (snow-flake): 2 separate fact tables

  9. Dimension Fact Snow flake schema

  10. Additivity • Can facts be added (summarized) across dimensions? • Fully additive (across all dimensions) • Sales, number of units sold • Semi-additive • Additive across some dimensions • E.g., account balances cannot be added across days • Non-additive

  11. Multiple stars • Basic idea: one process, one star • Different stars may be necessary when the business requires data • Of varying grains • Are measured at different intervals(order and shipping)

  12. Class exercise • Star schema of a hotel

  13. Homework 1B: Car maker DW • From A& V p.33 • Concerns: • Is minivan incentive ($200/minivan) working? • Are dealers abusing the lease option?

  14. Car maker DW • Measures = ? • Actual sales price • MSRP base price • Options price • Dealer add-ons • MSRP full price (=MSRP base + option) … • Dimension = ? • E.g., product

  15. Car maker DW • Queries can be created to address the concerns • Examples of Reports (p. 40, 41, 42)

  16. Summary • Review of Star Schema • Example • Class exercise • The DW design process (DW Vs OLTP)

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