Database Management - Boyce-Codd Normalization

8/7/2019 Database Management - Boyce-Codd Normalization

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BoyceBoyce--Codd NFCodd NFTakahiko SaitoTakahiko Saito

Spring 2005Spring 2005CS 157ACS 157A


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Purpose of NormalizationPurpose of Normalization

To reduce the chances for anomaliesTo reduce the chances for anomaliesto occur in a database.to occur in a database.

normalizationnormalization prevents the possibleprevents the possiblecorruption of databases stemmingcorruption of databases stemming

from what are called "insertionfrom what are called "insertionanomalies," "deletion anomalies," andanomalies," "deletion anomalies," and"update anomalies.""update anomalies."


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Insertion AnomalyInsertion Anomaly

A failure to place a new databaseA failure to place a new databaseentry into all the places in theentry into all the places in thedatabase where that new entry needsdatabase where that new entry needsto be stored.to be stored.

In a properly normalized database, aIn a properly normalized database, anew entry needs to be inserted intonew entry needs to be inserted into

only one place in the databaseonly one place in the database


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Deletion AnomalyDeletion Anomaly

A failure to remove an existingA failure to remove an existingdatabase entry when it is time todatabase entry when it is time toremove that entry.remove that entry.

In a properly normalized database,In a properly normalized database,

an old, toan old, to--bebe--gottengotten--ridrid--of entryof entryneeds to be deleted from only oneneeds to be deleted from only oneplace in the databaseplace in the database


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Update anomalyUpdate anomaly

An update of a database involvesAn update of a database involvesmodifications that may be additions,modifications that may be additions,

deletions, or both. Thus "updatedeletions, or both. Thus "updateanomalies" can be either of the kinds ofanomalies" can be either of the kinds ofanomalies discussed above.anomalies discussed above.


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1st Normal Form1st Normal Form

A table (relation) is in 1NF ifA table (relation) is in 1NF if1. There are no duplicated rows in the1. There are no duplicated rows in the

table.table.

2. Each cell is single2. Each cell is single--valuedvalued

3. Entries in a column are of the same3. Entries in a column are of the samekind.kind.


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2nd Normal Form2nd Normal Form

A table is in 2NF if it is in 1NF and if allA table is in 2NF if it is in 1NF and if allnonnon--key attributes are fully dependent onkey attributes are fully dependent on

each candidate key.each candidate key.

A partial dependency occurs when a nonA partial dependency occurs when a non--key attribute is dependent on only a partkey attribute is dependent on only a part

of the (composite) keyof the (composite) key


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1NF but not 2NF1NF but not 2NF

Supplier (Supplier (supplier#,supplier#, status, city,status, city, part#,part#,quantity)quantity)

(supplier#, part#)(supplier#, part#) --> quantity> quantity supplier#supplier# --> status> status

supplier#supplier# --> city> city

citycity --> status> status

=> status and city are dependent on just=> status and city are dependent on justpart of the key, namely supplier#.part of the key, namely supplier#.


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1NF but not 2NF (cont1NF but not 2NF (contd)d)

Decomposition (into 2NF):Decomposition (into 2NF):Supplier (supplier#, status, city)Supplier (supplier#, status, city)

Supplier_Part (supplier#, part#,Supplier_Part (supplier#, part#,quantity)quantity)


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3rd Normal Form (3NF)3rd Normal Form (3NF)

A table is in 3NF if it is in 2NF and if it hasA table is in 3NF if it is in 2NF and if it hasno transitive dependencies.no transitive dependencies.

Transitive dependency is a functionalTransitive dependency is a functionaldependency between nondependency between non--key attributes.key attributes.


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2NF but not 3NF2NF but not 3NF

Supplier (supplier#, status, city)Supplier (supplier#, status, city) supplier#supplier# --> status> status

supplier#supplier# --> city> city

citycity --> status> status

=> Lacks mutual independence among non=> Lacks mutual independence among non--keykey

attributes.attributes.


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2NF but not 3NF (cont2NF but not 3NF (contd)d)

Decomposition (into 3NF):Decomposition (into 3NF): SUPPLIER_CITY (supplier#, city)SUPPLIER_CITY (supplier#, city)

CITY_STATUS (city, status)CITY_STATUS (city, status)


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BoyceBoyce--Codd NFCodd NF

A table is in BCNF if it is in 3NF and ifA table is in BCNF if it is in 3NF and ifevery determinant is a candidate key.every determinant is a candidate key.

the definition of 3NF does not deal with athe definition of 3NF does not deal with arelation that:relation that:

has multiple candidate keys, wherehas multiple candidate keys, where

Those candidate keys are composite, andThose candidate keys are composite, and the candidate keys overlap (i.e., have at leastthe candidate keys overlap (i.e., have at least

one common attribute)one common attribute)


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3NF but not boyce3NF but not boyce--codd NFcodd NF

SUPPLIER_PART (supplier#, supplier_name,SUPPLIER_PART (supplier#, supplier_name,part#, quantity)part#, quantity) Two candidate keys:Two candidate keys:

(supplier#, part#) and (supplier_name, part#)(supplier#, part#) and (supplier_name, part#) (supplier#, part#)(supplier#, part#) --> quantity> quantity

(supplier#, part#)(supplier#, part#) --> supplier_name> supplier_name

(supplier#, part#)(supplier#, part#) --> quantity> quantity

(supplier#, part#)(s

upplier#, part#) --> s

upplier#> s

upplier# supplier_namesupplier_name --> supplier#> supplier#

supplier#supplier# --> supplier_name> supplier_name


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Another example of boyceAnother example of boyce--codd NFcodd NF

titletitle yearyear lengthlength filmTypefilmType studioNamstudioNamee

starNamestarName

Star WarsStar Wars 19771977 124124 colorcolor FoxFox FisherFisher

Star WarsStar Wars 19771977 124124 colorcolor FoxFox HamillHamill

Star WarsStar Wars 19771977 124124 colorcolor FoxFox FordFord

Mighty DucksMighty Ducks 19911991 104104 colorcolor DisneyDisney EstevesEsteves

WayneWaynes Worlds World 19921992 9595 colorcolor ParamountParamount CarveyCarvey

WayneWaynes Worlds World 19921992 9595 colorcolor ParamountParamount MeyersMeyers


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Example (contExample (contd)d)

{title, year, starName} as candidate key{title, year, starName} as candidate key title, yeartitle, year length, filmType, studioNamelength, filmType, studioName The above FD (Functional Dependency)The above FD (Functional Dependency)

violates the BCNF condition becauseviolates the BCNF condition because titletitleand yearand year do not determine the sixthdo not determine the sixth

attribute, starNameattribute, starName


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Example (contExample (contd)d)

We solve this BCNF violation by decomposingWe solve this BCNF violation by decomposingrelation Movies intorelation Movies into

1. The schema with all the attributes of the F

D1. The schema with all the attrib

utes of the F

D

{title, year, length, filmType,{title, year, length, filmType,studioName}studioName}

2. The schema with all attributes of Movies2. The schema with all attributes of Movies

except the three that appear on the right ofexcept the three that appear on the right ofthe FDthe FD

{title, year, starName}{title, year, starName}


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Summary of BoyceSummary of Boyce--Codd NFCodd NF

When there is more than one candidate key, a relationalWhen there is more than one candidate key, a relationaltable may be in 3NF and anomalies may still result.table may be in 3NF and anomalies may still result.

This occurs when there is a composite primary key, andThis occurs when there is a composite primary key, and

there are two equally valid candidates to make up partthere are two equally valid candidates to make up partof this composite primary key. If there is an attributeof this composite primary key. If there is an attribute(one or more columns) on which any other attribute is(one or more columns) on which any other attribute isfullyfully dependent, and this attribute is NOT itself adependent, and this attribute is NOT itself acandidate key, then the table is not incandidate key, then the table is not in BoyceBoyce--CoddCoddNormal formNormal form (BCNF).(BCNF).

We fix this by breaking the table up into two tables, bothWe fix this by breaking the table up into two tables, bothin BCNF.in BCNF.

Database Management - Boyce-Codd Normalization

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