texas state technical college discover! third normal form - 3nf it’s all about the key, the...
DESCRIPTION
Texas State Technical College DISCOVER! In order for a table to be considered 3NF, it must be 2NF and, consequentially, 1NF. In order for a table to be considered 3NF, all fields in the table must have NO Functional dependence upon non-key fieldsFunctional dependence upon non-key fields Transitive relationships to the primary keyTransitive relationships to the primary key Essentially, all fields must be directly related to or dependent upon the primary key. The Technical Definition Third Normal Form (3NF)TRANSCRIPT
Texas State Technical College
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Third Normal Form - 3NFThird Normal Form - 3NF
It’s all about the key, the whole key, and nothing
but the key.
Texas State Technical College
DISCOVER!
Third Normal Form (3NF)
3NF is a sufficient level of normalization for 3NF is a sufficient level of normalization for most databases.most databases.
At this point, the data is sufficiently At this point, the data is sufficiently organized to be useful as information to organized to be useful as information to most organizations or entities.most organizations or entities.
The focus of 3NF is to eliminate The focus of 3NF is to eliminate dependencies among non-key fields.dependencies among non-key fields.
OverviewOverview
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In order for a table to be considered 3NF, it In order for a table to be considered 3NF, it must be 2NF and, consequentially, 1NF.must be 2NF and, consequentially, 1NF.
In order for a table to be considered 3NF, all In order for a table to be considered 3NF, all fields in the table must have fields in the table must have NONO• Functional dependence upon non-key fieldsFunctional dependence upon non-key fields• Transitive relationships to the primary keyTransitive relationships to the primary key
Essentially, all fields must be directly Essentially, all fields must be directly related to or dependent upon the primary related to or dependent upon the primary key.key.
The Technical DefinitionThe Technical DefinitionThird Normal Form
(3NF)
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Functional dependenceFunctional dependence• Field Order_Total is dependent upon fieldsField Order_Total is dependent upon fields
• Order_QuantityOrder_Quantity• Order_Item_PriceOrder_Item_Price
• The functional dependence is defined asThe functional dependence is defined as• Order_Total = Order_Quantity X Order_Item_PriceOrder_Total = Order_Quantity X Order_Item_Price
Transitive dependenceTransitive dependence• Field Ship_Company is directly dependent uponField Ship_Company is directly dependent upon
• Shipment_ID Shipment_ID (primary key)(primary key)• Field Ship_Company_Address is dependent uponField Ship_Company_Address is dependent upon
• Ship_Company Ship_Company to link or relate toto link or relate to
• Shipment_IDShipment_ID
The Layman’s DefinitionThe Layman’s DefinitionThird Normal Form
(3NF)
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Functional dependenceFunctional dependence• Increases data redundancy and reduces independenceIncreases data redundancy and reduces independence• An update to one field requires update to othersAn update to one field requires update to others
Transitive dependenceTransitive dependence• Indicates a field is not describing the object represented Indicates a field is not describing the object represented
by the record or tableby the record or table• Field describes another object and should be in that Field describes another object and should be in that
object’s tableobject’s table
Why Eliminate …Why Eliminate …Third Normal Form
(3NF)
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For Example…For Example…Order
Order_IDpk Quantity Price TotalText Number Currency Currency
19568 4 4.00 16.00
85466 13 2.00 26.00
77788 10 30.00 300.00
ShipmentIDpk Provider Weight $perLB CostText Text Number Currency Currency
65664 FedEx 4.00 16.00 48.00
55555 USPS 2.00 2.00 4.00
87954 USPS 30.00 2.00 60.00
Two examples of functional
dependence.
Third Normal Form (3NF)
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For Example…For Example…Item
IDpk Mfg Address WeightText Text Text Number
19568 Bins 812 Bins Rd. 16.00
85466 B&D 113 Sears St. 26.00
77788 Shallot 888 9th St. 300.00
VehicleIDpk Enginefk MaxHP Make ModelText Text Number Text Text
65664 SVT-V8 340 Ford Cobra
55555 COT-82 115 Mercury Cougar
87954 CMN-99 220 Dodge Ram
Two examples of transitive
dependence.
Third Normal Form (3NF)
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1.1. For each field, identify its dependencies and their type.For each field, identify its dependencies and their type.
2.2. If it is a functional dependency on a non-key field, If it is a functional dependency on a non-key field, simply delete the dependent field.simply delete the dependent field.If there is a functional dependence, the value can be computed If there is a functional dependence, the value can be computed when the information is retrieved from the table.when the information is retrieved from the table.
3.3. If it is transitive dependence, treat it as a partial If it is transitive dependence, treat it as a partial dependence in 2NF.dependence in 2NF.Handle like in 2NF. Either move to the parent table or create a new Handle like in 2NF. Either move to the parent table or create a new table.table.
4.4. Repeat the process until database is 3NF.Repeat the process until database is 3NF.The database is 3NF when all tables in the database are 3NF.The database is 3NF when all tables in the database are 3NF.
Converting to 3NFConverting to 3NFThird Normal Form
(3NF)
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Corrected Example…Corrected Example…Order
Order_IDpk Quantity PriceText Number Currency
19568 4 4.00
85466 13 2.00
77788 10 30.00
ShipmentIDpk Provider Weight $perLBText Text Number Currency
65664 FedEx 4.00 16.00
55555 USPS 2.00 2.00
87954 USPS 30.00 2.00
Functional dependence:The dependent field has been discarded.
FIXED: The tables are now 3NF!
Third Normal Form (3NF)
Texas State Technical College
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Corrected Example…Corrected Example…
ItemIDpk Mfgfk WeightText Text Number
19568 Bins 16.00
85466 B&D 26.00
VehicleIDpk Enginefk Make ModelText Text Text Text
65664 SVT-V8 Ford Cobra
55555 COT-82 Mercury Cougar
87954 CMN-99 Dodge Ram
EngineIDpk MaxHPText Number
SVT-V8 340
COT-82 115
CMN-99 220
ManufacturerIDpk AddressText TextBins 812 Bins Rd.
B&D 113 Sears St.
Transitive dependence:The dependent field moved to own table.
FIXED: The tables are now 3NF!
Third Normal Form (3NF)
Texas State Technical College
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In Summary…In Summary…
• Third normal form (3NF) is defined asThird normal form (3NF) is defined as• 1NF and 2NF1NF and 2NF• Having no functional dependenciesHaving no functional dependencies• Having no transitive dependenciesHaving no transitive dependencies
• 3NF is a sufficient normalization for most 3NF is a sufficient normalization for most databases.databases.
• 3NF guarantees independence and 3NF guarantees independence and eliminates data redundancy.eliminates data redundancy.
Third Normal Form (3NF)