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Transcript of Modeling the Data Warehouse Chapter 7. Data Warehouse Database Design Phases zDefining the business...
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Modeling the Data Warehouse
Chapter 7
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Data Warehouse Database Design PhasesDefining the business
model (conceptual model)
Creating the dimensional model (logical model)
Modeling summariesCreating the physical
model
Select a businessprocess
Physical modelPhysical model
2,3
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Performing Strategic Analysis
Phase 1: Defining the Business Model
Select a businessprocess
�Performing strategic
analysis
�Creating the business
(conceptual) model
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Creating the Business Model
Phase 1: Defining the Business Model Performing strategic analysis Creating the business (conceptual)model - Defining business requirements - Identifying the business measures - Identifying the dimensions - Identifying the grain - Identifying the business definitions and rules - Verifying data sources
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Phase 1: Defining the Business Model
Creating the Business Model
Performing strategic analysis Creating the business (conceptual) model - Defining business requirements - Identifying the business measures - Identifying the dimensions - Identifying the grain - Identifying the business definitions and rules - Verifying data sources
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Business Requirements Drive the Design Process
Typ e tit le h ere Typ e tit le h ere Typ e tit le h ere
Typ e tit le h ere
Primary input
Other inputsBusiness requirements
Existingmetadata
ProductionERD model
Research Nonrelationallegacy systems
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Identifying Measures and Dimensions
The attribute variescontinuously: •Balance•United Sold•Cost•Sales
The attribute is perceived asa constant or discrete value:
•Description•Location•Color•Size
DimensionsMeasures
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Determining Granularity
YEAR?
QUARTER?
MONTH?
WEEK?
DAY?
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Identifying Business Rules
Location
Geographic proximity0 - 1 miles1 - 5 miles> 5 miles
Product
Type Monitor StatusPC 15 inch New
Server 17 inch Rebuilt 19 inch Custom
None
Time
Month>Quarter>Year
Store
Store>District>Region
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Creating the Dimensional Model
Identify fact tables - Translate business measures into fact tables - Analyze source system information for additional measures - Identify base and derived measures - Document additivity of measures Identify dimension tables Link fact tables to the dimension tables Create views for users
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Dimension Tables
Dimension tables have the following characteristics:Contain textual information that represents the
attributes of the businessContain relatively static dataAre joined to a fact table through a foreign key
reference
Facts(units, price)
Channel
Time
Product
Customer
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Fact Tables
Fact tables have the following characteristics: Contain numeric measures (metric) of the business May contain summarized (aggregated) data May contain date-stamped data Are typically additive Have key value that is typically a concatenated key
composed of the primary keys of the dimensions Joined to dimension tables through foreign keys that
reference primary keys in the dimension tables
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Facts(units, price)
Channel
Time
Product
Customer
Fact table
Dimension tables
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Star Schema Model
Central fact tableRadiating
dimensionsDenormalized
model
Sales Fact TableProduct_idStore_ idItem_idDay_idSales_dollarsSales_units
Product TableProduct_idProduct_desc
Store TableStore_idDistrict_id
Time TableDay_idMonth_idYear_id
Item TableItem_idItem_desc
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Star Schema Model
Easy for users to understandFast response to queriesSimple metadataSupported by many front end toolsLess robust to changeSlower to buildDoes not support history
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Snowflake Schema Model
Sales Fact TableProduct_idStore_ idItem_idDay_idSales_dollarsSales_units
Product TableProduct_idProduct_desc
Store TableStore_idDistrict_id
Time TableDay_idMonth_idYear_id
Item TableItem_idItem_desc
District TableDistrict_id
District_desc
Dept TableDept_id
Dept_descMgr_id
Mgr TableDept_idMgr_id
Mgr_name
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Snowflake Schema Model
Direct use by some toolsMore flexible to changeProvides for speedier data loadingMay become large and unmanageableDegrades query performanceMore complex metadata
Country State County City
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Using Summary Data
Phase 3: Modeling summariesProvides fast access to precomputed
dataReduces use of I/O, CPU, and memoryIs distilled from source systems and
precalculated summariesUsually exists in summary fact tables
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Designing Summary Tables
AverageMaximum
TotalPercentage
Units Sales($) Store
Product A Total
Product B Total
Product C Total
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Summary Tables Example
SALES FACTSSales$ Region Month10,000 North Jan 9912,000 North Feb 9911,000 South Jan 9915,000 West Mar 9918,000 South Feb 9920,000 North Jan 9910,000 East Jan 992,000 West Mar 99
SALES BY MONTH/REGIONMonth Region Tot_Sales$Jan 99 North 41,000Jan 99 East 10,000Feb 99 South 40,000Mar 99 West 17,000
SALES BY_MONTHMonth Tot_SalesJan 99 51,000Feb 99 40,000Mar 99 17,000
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Summary Management in Oracle8i
Summary advisor
Summaryrecommendations
Spacerequirements
Summaryusage
Region
State
City
Product Time
Salessummary
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Using Time in the Data Warehouse
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The Time Dimension
Time is critical to the data warehouseA consistent representation of time is
required for extensibility
Sales factTime
dimension
Where should the element of time be stored?
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Creating the Physical Model
Phase 4: Creating the Physical Model Translate the dimensional design to a physical
model for implementation Define storage strategy for tables and indexes Perform database sizing Define initial indexing strategy Define partitioning strategy Update metadata document with physical
information
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Physical Model Design Tasks
Define naming and database standardsPerform database sizingDesign tablespacesDevelop initial indexing strategyDevelop data partition strategyDefine storage parametersSet initialization parametersUse parallel processing
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Using Data Modeling Tools
Tools with a GUI enable definition, modeling, and reporting
Avoid a mix of modeling techniques caused by: - Development pressure - Developers with lack of knowledge - No strategyDetermine a strategyWrite and publish formallyMake available electronically
Spreadsheets
CASE tools Paper andpencil
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Summary
This lesson discussed the following topics:
Creating a business modelCreating a dimensional modelModeling the summariesCreating a physical model
Select among businessprocesses
Physical modelPhysical model
2,3
Business model
Dimensional model