Racoosin Solutions rSolutions@erols.com 703 849-1997

Database Normalization

TJ Racoosin

2 Dec 1998

CPCUG Access SIG

Overview

• Introductions

• The Normal Forms

• Primary Key

• Relationships and Referential Integrity

• When NOT to Normalize

• Real World Exercise

• Resources

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Introductions

• TJ Racoosin

• You– Are you familiar with normalization?– Used the relationship window ? Enforce

referential integrity? Cascade Delete?– Any issues with normalizing data?

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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 a

database into two or more tables and defining relationships between the tables.

• The objective is to isolate data so that additions, deletions, and modifications of a field can be made in 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 for storing information. Normalized data must 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• There’s 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

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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)

CustomersCustomerIDName

OrdersOrderIDItem CustomerIDOrderDate

Second Normal Form (2NF)• In 1NF and every non-key column is fully

dependent 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 and Date? Clue: repeating fields

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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

OrderDetailsOrderIDItem

OrdersOrderIDCustomerIDOrderDate

Third Normal Form (3NF)• In 2NF and every non-key column is mutually independent

– means : Calculations

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•Solution: Put calculations in queries and forms

Item Quantity Price TotalHammer 2 $10 $20Saw 5 $40 $200Nails 8 $1 $8

OrderDetailsOrderIDItemQuantityPrice

Put expression in text control or in query:=Quantity * Price

2/16/98 10MGS 404

2/16/98 10

Boyce-Codd Form (3NF) - Examples• A more restricted version of 3NF (known as

Boyce-Codd Normal Form) requires that the determinant of every functional dependency in a relation be a key - for every FD: X => Y, X is a 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

Primary Key

• Unique Identifier for every row in the table– Integers vice Text to save memory, increase

speed– Can be “composite”– Surrogate is best bet!

• Meaningless, numeric column acting as primary key in lieu of something like SSN or phone number - (both can be reissued!)

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Relationships

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• One to many to enforce “Referential Integrity”

Two “foreign” keys make a composite primary key and “relate” many to many tables

A look up table - it doesn’t reference any others

Table Prefixes Aid Development– First, we’ll 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” a “relational” table• trel “relational” (or junction or linking)

– two foreign keys make a primary

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tblOrdersOrderIDCustomerIDOrderDate

OrderDetailsOrderIDItem trelOrderItem

OrderIDItemID

tlkpItemsItemIDItemName

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– Can’t delete records from primary table if in related table

• Benefits - Data Integrity and Propagation– If update fields in main table, reflected in all queries– Can’t add a record in related table without adding it to main– Cascade Delete: If delete record from primary table, all

children deleted - use with care! Better idea to “archive”– Cascade Update: If change the primary key field, will change

foreign key

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When Not to Normalize• Want to keep tables simple so user can make

their 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 Data

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Student Student Previous CurrentLast First Parent 1 Parent 2 Teacher TeacherSmith 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 Phone5551 Private Hill Annandale Virginia 22003- (703) 323-08934902 Acme Ct Annandale Virginia 22003- (703) 764-58295304 Gains Street Fairfax Virginia 22032- (703) 978-1083 ….

First Year Last Year AgeProgram Enrolled Attended Birthday inSept Map Coord NotesPF / 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

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.htm

http://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

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