Data Data WarehouseWarehouse

Database Design Database Design MethodsMethods

For Technical IT For Technical IT AudienceAudience

Peter NolanPeter Nolanwww.peternolan.comwww.peternolan.com

Agenda

DW design methodsDW design methods Star SchemasStar Schemas

Why, What, Features?Why, What, Features?

Time Variant + Stability AnalysisTime Variant + Stability Analysis Why and What?Why and What?

DW Design Methods

Three different methods widely usedThree different methods widely used Choice of use depends on many factorsChoice of use depends on many factors Star SchemaStar Schema

Transaction and ROLAPTransaction and ROLAP

Time Variance + Stability AnalysisTime Variance + Stability Analysis Changes to non-txn data eg. CustomerChanges to non-txn data eg. Customer

Third Normal FormThird Normal Form Volumes of changes are lowVolumes of changes are low

Why Use Star Schemas?

Business people understand them!! Business people understand them!! Matches the business modelMatches the business model Often intuitively obviousOften intuitively obvious

Easy to queryEasy to query Supports complex questions easilySupports complex questions easily No wrong answers due to join problemsNo wrong answers due to join problems Excellent performance on star schema Excellent performance on star schema

aware databasesaware databases Oracle, Informix, DB2Oracle, Informix, DB2

What Does a Star Schema Look Like?

Time

Description

Day

Month

Year

Demogrph

Age

Sex

MaritalStatusGeocode

Postcode

Household

Accounts

Status

Category

Description

Branch

Name

Postcode

City

Region

State

Time

Demogrph

Accounts

Transactn

Branch

Amount

Cost

No Txns

Transactn

Code

Group

Debit/Credit

Some Useful Features

Multi-level summaries defined in control tableMulti-level summaries defined in control table New summaries require NO code changesNew summaries require NO code changes

Generated keys for customers and accountsGenerated keys for customers and accounts Demographic & Product Grouping for Demographic & Product Grouping for

customers and accountscustomers and accounts

Why Use Integer Keys?

PerformancePerformance Integers is the fastest data type to operate onIntegers is the fastest data type to operate on

Space and throughputSpace and throughput Integers are shorter than account numbersIntegers are shorter than account numbers Disk savings in tables and indexesDisk savings in tables and indexes Speed from disk to processorSpeed from disk to processor

FlexibilityFlexibility Allows multi-level summary tablesAllows multi-level summary tables No IT involvement to create new summaries!!No IT involvement to create new summaries!!

Large Stars!!Large Stars!!

Why Use TV + SA?

““Be able to show me the value of any field at Be able to show me the value of any field at any time in the past”any time in the past”

Archival databasesArchival databases When people really do not know what they When people really do not know what they

wantwant Not easy to query Not easy to query

Cannot give this to business peopleCannot give this to business people

What Does TV + SA Look Like?

Each 3NF entity passed to the DW is split into 3 (or more) entities based on stability analysis and access analysis.An element of time is added to the key.

Natural Key

Date From

Date To

Highly

VolatileDataElements

Natural Key

Date From

Date To

Medium

VolatileDataElements

Natural Key

Date From

Date To

Low

VolatileDataElements

Summary

DW design methodsDW design methods Star SchemasStar Schemas

Why, What Features?Why, What Features?

Time Variant + Stability AnalysisTime Variant + Stability Analysis Why and What?Why and What?

Thank You for Your Thank You for Your Time!Time!