Normal Forms By Christopher Archibald October 16 th 2007

Normal FormsNormal Forms

By Christopher ArchibaldBy Christopher Archibald

October 16October 16thth 2007 2007

OverviewOverview

Database NormalizationDatabase Normalization

11stst Normal Form Normal Form

22ndnd Normal Form Normal Form

33rdrd Normal Form Normal Form

Boyce- Codd Normal Form (BCNF)Boyce- Codd Normal Form (BCNF)

Lossless-JoinLossless-Join

NormalizationNormalization

Normalization is a technique for designing Normalization is a technique for designing relational table to:relational table to: Minimize duplication of informationMinimize duplication of information Reduce the potential for data anomaliesReduce the potential for data anomalies

Normal FormNormal Form

Normal forms provide a stepwise Normal forms provide a stepwise progression toward the goal of fully progression toward the goal of fully normalized relation schema that are free normalized relation schema that are free for data redundancies.for data redundancies.

First Normal Form (1NF)First Normal Form (1NF)

1NF definition: A schema R is in 1NF only 1NF definition: A schema R is in 1NF only when the attributes comprising the when the attributes comprising the schema are atomic and single-valuedschema are atomic and single-valued No Multi-valued attributesNo Multi-valued attributes No composite attributesNo composite attributes No repeating groups (2 columns can not store No repeating groups (2 columns can not store

similar information)similar information) Can’t have a Null AttributeCan’t have a Null Attribute Must have a Primary KeyMust have a Primary Key

First Normal Form First Normal Form ExampleExample

This is in 1NF (Has primary Key, no repeating This is in 1NF (Has primary Key, no repeating group, No Null attributes and No multivariablegroup, No Null attributes and No multivariable

What happens if James gets a Second Phone What happens if James gets a Second Phone Number?Number?

First Normal FormFirst Normal FormExampleExample

No longer in 1NF because Telephone Number No longer in 1NF because Telephone Number has a multivariable.has a multivariable.

Now we need to redesign our tableNow we need to redesign our table

First Normal FormFirst Normal FormExampleExample

Not in First Normal forumNot in First Normal forum Tel. No. 3 is a null attributeTel. No. 3 is a null attribute Tel. No. 1-2 repeat similar information (Repeating Tel. No. 1-2 repeat similar information (Repeating

group)group)

First Normal FormFirst Normal Form

This is in First Normal This is in First Normal FormForm

Telephone Number is Telephone Number is no long a repeating no long a repeating groupgroup

No MultivariableNo Multivariable

No Null AttributesNo Null Attributes

Has a Primary KeyHas a Primary Key

Second Normal Form (2NF)Second Normal Form (2NF)

2NF Definition: A relation schema R is in 2NF Definition: A relation schema R is in 2NF if every non-prime attribute in R is 2NF if every non-prime attribute in R is fully functionally dependent on the primary fully functionally dependent on the primary key of R.key of R. Must be 1NFMust be 1NF An Attribute that is not part of the candidate An Attribute that is not part of the candidate

key must be dependent on the candidate key key must be dependent on the candidate key and not a part of the candidate keyand not a part of the candidate key

Second Normal FormSecond Normal FormExampleExample

Only Candidate key is Only Candidate key is (Employee, Skill)(Employee, Skill)

Not in 2NFNot in 2NF

Current Work Location is Current Work Location is dependent on Employeedependent on Employee

Can Cause an AnomalyCan Cause an Anomaly

Updating Jones Work location for Typing and Shorthand but not Whittling. Then asking “What is Jones current work location”, can cause a contradictory answer, because there are 2 different locations.

Second Normal Form Second Normal Form ExampleExample

Both tables are in Both tables are in 2NF2NF

Meets 1NF Meets 1NF requirementsrequirements

No non-primary key No non-primary key attribute is dependent attribute is dependent on part of a key.on part of a key.

1NF and 2NF1NF and 2NF1NF and 2NF remove most anomalies1NF and 2NF remove most anomalies

Following table is in 2NFFollowing table is in 2NF

There is redundancy under Winner/Winner DoBThere is redundancy under Winner/Winner DoB Al Fredrickson and Chip MastersonAl Fredrickson and Chip Masterson Can cause an anomalyCan cause an anomaly

Third Normal Form (3NF)Third Normal Form (3NF)

3NF Definition: A relation schema R is in 3NF Definition: A relation schema R is in 3NF if no non-prime attribute is 3NF if no non-prime attribute is functionally dependent on another non-functionally dependent on another non-prime attribute in Rprime attribute in R Table must be in 2NFTable must be in 2NF Eliminate field that do not depended on the Eliminate field that do not depended on the

primary key by placing them in different tablesprimary key by placing them in different tables

Third Normal FormThird Normal FormExampleExample

Table is in 2NF but fails to meet 3NFTable is in 2NF but fails to meet 3NFWinner Date of Birth is Dependent on WinnerWinner Date of Birth is Dependent on Winner If Al Fredrickson Date of birth is update in the first row If Al Fredrickson Date of birth is update in the first row

but not the second ask, “What Al Fredrickson Date of but not the second ask, “What Al Fredrickson Date of birth” will result in 2 different dates.birth” will result in 2 different dates.

Third Normal FormThird Normal FormExampleExample

Table is in 3NFTable is in 3NF Meets 1NF and 2NFMeets 1NF and 2NF No non-primary Key No non-primary Key

attribute is Dependent attribute is Dependent on another non-on another non-primary Key attributeprimary Key attribute

Update Anomalies Update Anomalies cannot occur in these cannot occur in these tablestables

Boyce-Codd Normal Form (BCNF)Boyce-Codd Normal Form (BCNF)

BCNF Definition: A relation Schema R is BCNF Definition: A relation Schema R is in BCNF if for every non-trivial functional in BCNF if for every non-trivial functional dependency in R, the determinant is a dependency in R, the determinant is a superkey of Rsuperkey of R Does not allow Functional Dependency that is Does not allow Functional Dependency that is

not part of a Candidate keynot part of a Candidate key

Most 3NF meet the requirement of a Most 3NF meet the requirement of a BCNFBCNF

Boyce-Codd Normal FormBoyce-Codd Normal FormExampleExample

Candidate key (Tutor ID, Student ID) And (SSN, Candidate key (Tutor ID, Student ID) And (SSN, Student ID)Student ID)

Table is in 3NF, but not BCNFTable is in 3NF, but not BCNF

SNN is dependent on Tutor ID but (Tutor id, SNN) is SNN is dependent on Tutor ID but (Tutor id, SNN) is not a Candidate keynot a Candidate key

Other Normal FormsOther Normal Forms

There is alsoThere is also Fourth normal formFourth normal form Fifth normal FormFifth normal Form Domain/key Normal formDomain/key Normal form Sixth normal formSixth normal form

Which will be covered in chapter 9Which will be covered in chapter 9

Lossless-Join DecompositionLossless-Join Decomposition

The principle behind Lossless-Join The principle behind Lossless-Join decomposition is that the decomposition of decomposition is that the decomposition of a relation schema, R, should be strictly a relation schema, R, should be strictly reversible, i.e.reversible, i.e.

When we break tuples in to different tables When we break tuples in to different tables for normalization we should be able to for normalization we should be able to combined them and get what we startedcombined them and get what we started


Flight #Flight # OriginOrigin DestinationDestination MileageMileage

DL723DL723 BostonBoston St. LouisSt. Louis 12141214

DL577DL577 DenverDenver Los AngelesLos Angeles 11001100

DL5219DL5219 MinneapolisMinneapolis St. LouisSt. Louis 580580

DL357DL357 ChicagoChicago DallasDallas 10581058

DL555DL555 DenverDenver HoustonHouston 11001100

DL5237DL5237 ClevelandCleveland St. LouisSt. Louis 580580


OriginOrigin DestinationDestination MileageMileage

BostonBoston St. LouisSt. Louis 12141214

DenverDenver Los AngelesLos Angeles 11001100

MinneapolisMinneapolis St. LouisSt. Louis 580580

ChicagoChicago DallasDallas 10581058

DenverDenver HoustonHouston 11001100

ClevelandCleveland St. LouisSt. Louis 580580

Flight #Flight # MileageMileage

DL723DL723 12141214

DL577DL577 11001100

DL5219DL5219 580580

DL357DL357 10581058

DL555DL555 11001100

DL5237DL5237 580580

Lossless-Join DecompositionLossless-Join DecompositionFlight #Flight # OriginOrigin DestinationDestination MileageMileage

DL723DL723 BostonBoston St. LouisSt. Louis 12141214

DL577DL577 DenverDenver Los AngelesLos Angeles 11001100




DL357DL357 ChicagoChicago DallasDallas 10581058

DL555DL555 DenverDenver Lost AngelesLost Angeles 11001100




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Normal Forms By Christopher Archibald October 16 th 2007