Comparison between ER Modeling and Dimension Modeling

1. Comparative Study of E-R Modeling and Dimensional Modeling
PRN
NAME
12030121020
Shivam Tyagi
12030121026
Aniket Srivastava
12030121028
Amit Shivsharan
12030121030
Karuna Kak
BCA (2012-15)
Division A

2. Entity Relationship Modeling
•Theentity-relationship(E-R)datamodelisbasedonaperceptionofarealworldthatconsistsofasetofbasicobjectscalledentities,andofrelationshipsamongtheseobjects.
•StepsinE-RModeling:
Identify the entitiesLook for general Nouns in requirement specification document, which are of business interest to users.
IdentifythekeyattributesforeveryentityIdentifytheattributeorsetofattributeswhichcanidentifyinstanceofentityuniquely
Find the associations between entitiesIdentify the natural relationship and their cardinalities between the entities.
Complete E-R Diagram Draw complete ER diagram with all attributes including primary key .
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Symbol
Description

4. E-R Modeling Example
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5. Star schema
•Starschemaisadimensionmodelingtechnique.
•ThedimensiontablearerelatedtoeachotherwithM:Mrelationshipandaredenormalized.
•ThefacttableisnormalisedbecauseithasI:Mrelationshipwithotherdimensions.
•Example:Items,Branch,Location,andTimeareDimensionTableswhicharedenormalized.Totalsaleswithtime_key,item_key, branch_keyandlocation_key(primarykeysofalldimensiontables)istheFactTablewhichisnormalized.
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Star Schema Example

7. Snowflake schema
•Thesnowflakeschemaisadimensionmodelingtechnique.
•"Snowflaking"isamethodofnormalisingthedimensiontablesinastarschema.Dimensiontablesgetpartiallynormalised.
•Theprinciplebehindsnowflakingisnormalisationofthedimensiontablesbyremovinglowcardinalityattributesandformingseparatetables.
•Whenwedonotaccessaparticulartableorwedon’tretrieveanythingfromthetablefrequently,webreakthetablewith1:Mrelationship.
•Example:Items,Branch,Location,andTimeareDimensionTableswhicharedenormalized.Totalsaleswithtime_key,item_key,branch_keyandlocation_key(primarykeysofalldimensiontables)istheFactTablewhichisnormalized.Alsoitemsdimensionhadcityfieldsandlocationdimensionhadacityfieldswhichwereretrievedveryinfrequentlythereforetheyarebreakdownintoseparatedimensiontables.
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8. 8
Snowflake Schema Example

9. Comparative Study of ER Modeling and Dimensional Modeling
E-R Modeling
Dimensional Modeling
SupportsOLTP(OnlineTransactionProcessing)
SupportsOLAP(OnlineAnalyticalProcessing)
Entitiesarelinkedwithaseriesofjoins.
Entitiesarelinkedwithaseriesofjoins.
Normalized
Denormalized
Removesredundancy.
Permitsredundancy.
Ifmodelismodified,theapplicationaremodified.
Itisextensibletoaccommodateunexpectednewdataelementsandnewdesigndecision.
Itisvariableinstructureandveryvulnerabletochangesintheuser’squeryinghabits.
Itisrobust.Thedimensionalmodeldesigncanbedoneindependentofexpectedquerypattern.
Themodelforenterpriseisveryhardforpeopletovisualizeandkeepintheirheads.
Thismodeliseasyandunderstandable.