Normalization Venu

8/6/2019 Normalization Venu

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Database Normalization

A. Venu Gopal

22 Feb 2011

Himansu IT Services


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Overview Introductions

The Normal Forms Primary Key

Relationships and Referential Integrity

When NOT to Normalize Real World Exercise

Resources

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Why Normalize? Flexibility

Structure supports many ways to look at the data

Data Integrity Modification Anomalies

Deletion

Insertion

Update

Efficiency

Eliminate redundant data and save space

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Normalization Defined In relational database design, the process of

organizing data to minimize duplication.

Normalization usually involves dividing adatabase into two or more tables and definingrelationships between the tables.

The objective is to isolate data so that additions,

deletions, and modifications of a field can be madein just one table and then propagated through the

rest of the database via the defined relationships.- Webopedia, http://webopedia.internet.com/TERM/n/normalization.html

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Another Definition "Normalization" refers to the process of

creating an efficient, reliable, flexible,

and appropriate "relational" structure forstoring information. Normalized datamust be in a "relational" data structure.

- Reid Software Development, http://www.accessdatabase.com/normalize.html

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The Normal Forms A series of logical steps to take to

normalize data tables

First Normal Form Second

Third

Boyce Codd Theres more, but beyond scope of this

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First Normal Form (1NF) All columns (fields) must be atomic

Means : no repeating items in columns

OrderDate Customer Items11/30/1998 Joe Smith Hammer, Saw, Nails

OrderDate Customer Item1 Item2 Item311/30/1998 Joe Smith Hammer Saw Nails

Solution: make a separate table for each set of

attributes with a primary key (parser, append query)Customers

CustomerID

Name

Orders

OrderID

Item

CustomerID

OrderDate Himansu IT Services


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Second Normal Form ( NF) In 1NF and every non-key column is fullydependent on the (entire) primary key Means : Do(es) the key field(s) imply the rest of the fields? Do we

need to know both OrderID and Item to know the Customer andDate? Clue: repeating fields

Solution: Remove to a separate table (Make Table)

OrderID Item CustomerID OrderDate1 Hammer 1 11/30/19981 Saw 1 11/30/19981 Nails 1 11/30/1998

OrderDetails

OrderID

Item

Orders

OrderID

CustomerID

OrderDateHimansu IT Services


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Third Normal Form (3NF) In NF and every non-key column is mutually

independent

means : Calculations

Solution: Put calculations in queries and forms

Item Quantity Price TotalHammer $10 $ 0Saw 5 $40 $ 00Nails 8 $1 $8

OrderDetailsOrderID

Item

Quantity

Price

Putexpressionintextcontrolorin query:

=Quantity * Price

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2/16/98 10MGS 4042/16/98 10

Boyce-Codd Form (3NF) - Examples

A more restricted version of 3NF (known asBoyce-Codd Normal Form) requires that thedeterminant of every functional dependency ina relation be a key - for every FD: X => Y, X isa key

Consider the following relation:STU-MAJ-ADV (Student-Id, Major, Advisor)

Advisor => Major, but Advisor is not a key Boyce-Codd Normal Form for above:

STU-ADV (Student-Id, Advisor)ADV-MAJ (Advisor, Major)

Kumar Madurai: http://www.mgt.buffalo.edu/courses/mgs/404/mfc/lecture4.ppt


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Primary Key Unique Identifier for every row in the

table

Integers vice Text to save memory, increasespeed

Can be composite

Surrogate is best bet!

Meaningless, numeric column acting asprimary key in lieu of something like SSN orphone number - (both can be reissued!)

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Relationships One to many to enforce Referential Integrity

Two foreign

keys make acomposite primary

key and relate

many to many

tables

A lookup table - it

doesnt reference

any others

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Table Prefixes Aid Development

First, well get replace text PK with number

The Items table is a look up with tlkp prefix tlkp lookup table (no foreign keys)

OrderDetails is renamed trelOrderItem arelational table trel relational (or junction or linking)

two foreign keys make a primary

tblOrders

OrderID

CustomerID

OrderDate

OrderDetails

OrderID

Item trelOrderItem

OrderID

ItemID

tlkpItems

ItemID

ItemName

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Referential Integrity Every piece of foreign key data has a

primary key on the one site of the relationship No orphan records. Every child has a parent

Cant delete records from primary table if in related table

Benefits - Data Integrity and Propagation If update fields in main table, reflected in all queries

Cant add a record in related table without adding it to main

Cascade Delete: If delete record from primary table, allchildren deleted - use with care! Better idea to archive

Cascade Update: If change the primary key field, will changeforeign key

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When Not to Normalize

Want to keep tables simple so user can maketheir own queries Avoid processing multiple tables

Archiving Records If No need to perform complex queries or resurrect

Flatten and store in one or more tables

Testing shows Normalization has poorer

performance Sounds Like field example

Can also try temp tables produced from Make Table queries

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Real World - School DataStudent Student Previous Current

Last First Parent 1 Parent 2 Teacher Teacher

Smith Renee Ann Jones Theodore Smith Hamil BurkeMills Lucy Barbara Mills Steve Mills Hamil Burke

Jones Brendan Jennifer Jones Stephen Jones Hamil Burke.

Street Address City State Postal Code Home Phone

5551 Private Hill Annandale Virginia 22003- (703) 323-08934902 Acme Ct Annandale Virginia 22003- (703) 764-5829

5304 Gains Street Fairfax Virginia 22032- (703) 978-1083 .

First Year Last Year Age

Program Enrolled Attended Birthday inSept Map Coord Notes

PF / 0 0 6/25/93 5 22 A-3PF 96/97 0 8/14/93 5 21 F-3PH 96/97 0 6/13/94 4 21 A-4

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One Possible Design

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Books Access97 Developers Handbook Litwin,Getz & Gilbert Chapter 4

Access and SQL Server Developers Handbook

Viescas, Gunderloy and Chipman Chapter 2

Access97 Expert Solutions Lezynski Chapter 10

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Internet Papers http://www.mtjeff.com/~calvin/devhbook/databasedesign.html

http://www.swin.edu.au/infotech/subjects/bt220/bt220s1.html

http://www.bus.okstate.edu/lhammer/AISweb/Normaliz.htmhttp://www.inetspace.com/database.html

Slides http://www.mgt.buffalo.edu/courses/mgs/404/mfc/lecture4.ppt

http://www.state.sd.us/people/colink/datanorm.htm

http://www.cba.nau.edu/morgan-j/class/subtop2_3/sld001.htm

R

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