DSS Schemas

E D U C A T I O N

DSS SchemasDSS Schemas

E D U C A T I O N

DSS Schemas -- AgendaDSS Schemas -- Agenda

• The Consolidated Star

• The Normalized Star (Snowflake)

E D U C A T I O N

Fact Sales

Product Time

Day

Month

Year

Geography

Store

Market

Region

Example Logical ModelExample Logical Model

Item

Class

Dept

Division

E D U C A T I O N

Lookup Product

Product_keyProduct_descItem_idClass_idDept_idDivision_idLevel

Lookup Geography

Geo_keyGeo_descStore_idMarket_idRegion_idLevel

Fact Sales

Product_keyGeo_keyTime_keySales_DollarsSales_Units

Lookup Time

Time_keyTime_descDateMonth_idYear_idLevel

Consolidated Star Schema (1)Consolidated Star Schema (1)

E D U C A T I O N

Star #1

GEO_KEY GEO_DESC STORE_ID MARKET_ID REGION_ID LEVEL

1001 Boston 101 20 1 1

1002 Greenwich 102 20 1 1

1003 Providence 103 20 1 1

1004 Baltimore 104 10 1 1

1005 Philadelphia 105 10 1 1

1006 Charlotte 106 30 2 1

1007 Durham 107 30 2 1

1008 Greenville 108 30 2 1

1009 Atlanta 109 40 2 1

1010 Fayetteville 110 40 2 1

1011 Mid-Atlantic 10 1 2

1012 New England 20 1 2

1013 Carolinas 30 2 2

1014 Deep South 40 2 2

1015 Northeast 1 3

1016 South 2 3

Consolidated Star Schema LookupsConsolidated Star Schema Lookups

Lookup Geography


Generic dimension key Null fields Level flag

E D U C A T I O N

• How do we get the following desired report?

Limitation of Consolidated Star (1)Limitation of Consolidated Star (1)

Sales $

1,000 1,000 1,000 2,0002,0002,000

Region

NortheastNortheast Northeast SouthSouth South

Store

BostonPhillyBaltimoreCharlotteAtlantaDurham

SELECT a1.Geo_desc Region, a2.Geo_desc StoreFROM LU_Geo a1, LU_Geo a2, Fact a3WHEREa1.Geo_Key = a2.Geo_Key

a2.Geo_Key = a3.Geo_Keya1.level = 3a2.level = 1

GROUP BY Region, Store

Lookup Geography


Fact Sales


Necessary Tables:

• Self-join is necessary.

• Self-joins are generally undesirable.

E D U C A T I O N

Lookup Product

Product_keyItem_descClass_descDept_descDivision_descLevel

Lookup Geography

Geo_keyStore_descMarket_descRegion_descLevel

Fact Sales


Lookup Time

Time_keyDateMonth_descYear_idLevel


E D U C A T I O N

Lookup Product

Product_keyItem_idItem_descClass_idClass_descDept_idDept_descDivision_idDivision_descLevel

Lookup Geography

Geo_keyStore_idStore_descMarket_idMarket_descRegion_idRegion_descLevel

Fact Sales


Lookup Time

Time_keyDateMonth_idMonth_descYear_idLevel


E D U C A T I O N

Cons. Star #1 Cons. Star #2 Cons. Star #3

Consolidated Star Lookup ComparisonConsolidated Star Lookup Comparison

Lookup Geography

Geo_keyStore_idStore_descMarket_idMarket_descRegion_idRegion_descLevel

Lookup Geography

Geo_keyStore_descMarket_descRegion_descLevel

Lookup Geography


E D U C A T I O N

Time_key

DateDateDateDate DateDateDateDateDateDateDateDate Month...

Fact Sales

Product_keyGeo_keyTime_keySales_Dollars

Consolidated Star Schema Fact TablesConsolidated Star Schema Fact Tables

Product_key

ItemClassDeptDivisionItemClassDeptDivision ItemClassDeptDivision Item...

Geo_key

Store Store StoreStoreMarketMarketMarketMarketRegionRegion Region Region Store...

Contains all possible levels of

data.

Sales

1002003005002003505006005004507509001500...

E D U C A T I O N

Lookup Product

Product_keyProduct_descItem_idClass_idDept_idDivision_idLevel

Lookup Geography


Fact Sales


Lookup Time

Time_keyTime_descDateMonth_idYear_idLevel

Consolidated Star Schema SummaryConsolidated Star Schema Summary

Select Product_desc, Geo_desc, Time_desc, Sales_Dollars, Sales_UnitsFrom Fact_Sales F,

Lookup_Product P, Lookup_Geography G, Lookup_Time T

Where F.Product_key = P.Product_keyAnd F.Geo_key = G.Geo_keyAnd F.Time_key = T.Time_keyAnd G.Level = ??And P.Level = ??And T.Level = ??

E D U C A T I O N

Normalized Star Schema (1)Normalized Star Schema (1)

Fact Sales

Item_idStore_idDateSales_DollarsSales_Units

Lookup Division

Division_idDivision_desc

Lookup Dept

Dept_idDept_descDivision_id

Lookup Class

Class_idClass_descDept_id

Lookup Item

Item_idItem_descClass_id

Lookup Store

Store_idStore_descMarket_id

Lookup Market

Market_idMarket_descRegion_id

Lookup Region

Region_idRegion_desc

Lookup Day

DateMonth_id

Lookup Month

Month_idMonth_descYear_id

Lookup Year

Year_id

E D U C A T I O N

Normalized Star #1

REGION_ID REGION_DESC

1 Northeast

2 South

MARKET_ID MARKET_DESC REGION_ID

10 Mid-Atlantic 1

20 New England 1

30 Carolinas 2

40 Deep South 2

STORE_ID STORE_DESC MARKET_ID

101 Boston 20

102 Greenwich 20

103 Providence 20

104 Baltimore 10

105 Philadelphia 10

106 Charlotte 30

107 Durham 30

108 Greenville 30

109 Atlanta 40

110 Fayetteville 40

Lookup Store


Lookup Market


Lookup Region


Normalized Star Schema LookupsNormalized Star Schema Lookups

E D U C A T I O N


Fact Sales


Lookup Division


Lookup Dept

Dept_idDept_descDivision_id

Lookup Class

Class_idClass_descDept_idDivision_id

Lookup Item

Item_idItem_descClass_idDept_idDivision_id

Lookup Store

Store_idStore_descMarket_idRegion_id

Lookup Market


Lookup Region


Lookup Day

DateMonth_idYear_id

Lookup Month


Lookup Year

Year_id

E D U C A T I O N

Normalized Star #2

REGION_ID REGION_DESC

1 Northeast

2 South

MARKET_ID MARKET_DESC REGION_ID

10 Mid-Atlantic 1

20 New England 1

30 Carolinas 2

40 Deep South 2

Lookup Store


Lookup Market


Lookup Region


Normalized Star Schema Lookups (2)Normalized Star Schema Lookups (2)

STORE_ID STORE_DESC MARKET_ID REGION_ID

101 Boston 20 1

102 Greenwich 20 1

103 Providence 20 1

104 Baltimore 10 1

105 Philadelphia 10 1

106 Charlotte 30 2

107 Durham 30 2

108 Greenville 30 2

109 Atlanta 40 2

110 Fayetteville 40 2

Denormalized attribute id

column

E D U C A T I O N


Fact Sales


Lookup Division


Lookup Dept

Dept_idDept_descDivision_idDivision_desc

Lookup Class

Class_idClass_descDept_idDept_descDivision_idDivision_desc

Lookup Item

Item_idItem_descClass_idClass_descDept_idDept_descDivision_idDivision_desc

Lookup Store

Store_idStore_descMarket_idMarket_descRegion_idRegion_desc

Lookup Market

Market_idMarket_descRegion_idRegion_desc

Lookup Region


Lookup Day

DateMonth_idMonth_descYear_id

Lookup Month


Lookup Year

Year_id

E D U C A T I O N

Snowflake #1 Snowflake #2 Snowflake #3

Lookup Store


Lookup Store


Lookup Store


Normalized Star Lookups ComparisonNormalized Star Lookups Comparison

E D U C A T I O N

Atomic level data Aggregate level data

Fact Sales - Stores


Normalized Star Schema Fact TablesNormalized Star Schema Fact Tables

Fact Sales - Markets

Item_idMarket_idDateSales_DollarsSales_Units

Fact Sales - Regions

Item_idRegion_idDateSales_DollarsSales_Units

E D U C A T I O N

Why ‘Higher Level’ Attribute Lookup Tables?Why ‘Higher Level’ Attribute Lookup Tables?

• Below is pictured a Snowflake Schema without any higher-level lookup tables. Note its similarity to the Consolidated Star Schema.

• Consider the questions below.

Fact Sales - Stores




Lookup Item


Lookup Store


Lookup Day


E D U C A T I O N

• Higher level lookup tables provide for more efficient browsing.

• Higher level lookup tables are what enable the use of aggregate fact tables.

Fact Sales - Stores




Lookup Division


Lookup Dept


Lookup Item


Lookup Store


Lookup Region


Lookup Day


Why ‘Higher Level’ Attribute Lookup TablesWhy ‘Higher Level’ Attribute Lookup Tables

E D U C A T I O N

Fact Sales - Stores


Normalized Star Schema SummaryNormalized Star Schema Summary



Lookup Division


Lookup Dept


Lookup Item


Lookup Store


Lookup Region


Lookup Day


E D U C A T I O N

• Consolidated Star

• Few Tables / Few Joins

• Easy SQL

• No support for M:M relationships

• Limited support for characteristic attributes

• Inflexible schema

• Not scalable

The Consolidated Star vs.The SnowflakeThe Consolidated Star vs.The Snowflake

• Snowflake

• More Tables / More Joins

• More complex SQL

• M:M is possible

• Characteristic attributes fully supported

• Flexible schema

• Scalable

vs.

E D U C A T I O N

Continue Case StudyContinue Case Study

• Continue working on the Case Study.

DSS Schemas

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