IT420: Database Management and
Organization
Normalization
31 January 2006
Adina Cr ăiniceanu www.cs.usna.edu/~adina

 Database design
 Entity-Relationship (ER) Model
 Relational Model
 Transform ER to relational model
 Database Implementation
 SQL
Kroenke, Database Processing

 Refresh ER to Relational
 Normalization
Kroenke, Database Processing

 ER:
 Entities
 identifiers
 Relationships
 cardinality
 Relational model
 Tables
 Constraints
Kroenke, Database Processing

 Transform entities in tables
 Transform relationships using foreign keys
 Specify logic for enforcing minimum cardinalities
Kroenke, Database Processing

Class Exercise: Transform ER model into Relational Model
CLUB
FAALicense
AIRCRAFT
FAA number
Address
Phone ModelNumber
Color
Min Cardinality:1
OWNER
Name
Phone
Min Cardinality:1 Address
MEMBER
Name
Phone
Rating
TotalHours
FLIGHT
FlightID
RentalDate
ReturnDate
TimeFlown
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 ER to Relational
 Normalization
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 We have received one or more tables with data
 The data is to be stored in a new database
 QUESTION: Should the data be stored as received, or should it be transformed for storage?
Kroenke, Database Processing

Number LastName FirstName
190
673
312
Smith
Doe
Doe
John
Jane
Bob
Email jsmith@usna.edu
jdoe@usna.edu
bred@usna.edu
152 Johnson Matt mat@usna.edu
Rating
4
7
8
7
Wage
25
35
40
35
Application constraint:
All employees with same rating have the same wage (Rating  Wage)
Problems due to data redundancy?
Kroenke, Database Processing

 Deletion Anomaly : What if we delete all employees with rating 8?
 Insertion Anomaly : What if we have a new employee with new rating 12?
 Update Anomaly : What if we change the wage for rating 7 to be 27?
Kroenke, Database Processing

 The EMPLOYEE table before and after an incorrect update operation on Wage for Rating = 7
Number LastName FirstName
190
673
312
Smith
Doe
Doe
John
Jane
Bob
152 Johnson Matt
Email jsmith@usna.edu
jdoe@usna.edu
bred@usna.edu
mat@usna.edu
Rating
4
7
8
7
Number LastName FirstName
190
673
312
Smith
Doe
Doe
John
Jane
Bob
152 Johnson Matt
Email jsmith@usna.edu
jdoe@usna.edu
bred@usna.edu
mat@usna.edu
Kroenke, Database Processing
7
Rating
4
7
8
Wage
25
35
40
35
Wage
25
37
40
35

Number LastName FirstName
190 Smith John
673
312
Doe
Doe
Jane
Bob
152 Johnson Matt
Email jsmith@usna.edu
jdoe@usna.edu
bred@usna.edu
mat@usna.edu
Rating
4
7
8
7
Wage
25
35
40
35
Number LastName FirstName
190 Smith John
Email jsmith@usna.edu
673
312
Doe
Doe
152 Johnson
Jane
Bob
Matt jdoe@usna.edu
bred@usna.edu
mat@usna.edu
Rating
4
7
8
7
Kroenke, Database Processing
Rating
4
7
8
Wage
25
35
40
Problem?

 Do we have to decompose / merge?
 How do we identify problems caused by redundancy?
 Functional dependencies
Kroenke, Database Processing

 A functional dependency: the value of one (a set of) attribute(s) determines the value of a second (set of) attribute(s):
Alpha  MIDNName
Alpha  (DormName, DormRoom)
 The attribute on the left side of the functional dependency is called the determinant
 Functional dependencies may be based on equations:
Charge = NbHours X HourlyPrice
(NbHours, HourlyPrice)  Charge
 Function dependencies are not equations!
Kroenke, Database Processing

Functional Dependencies Are Not Equations
ObjectColor  Weight
ObjectColor  Shape
ObjectColor  (Weight, Shape)
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 Composite determinant : A determinant of a functional dependency that consists of more than one attribute
 (StudentName, ClassName)  Grade
 (NbHours, HourlyPrice)  Charge
Kroenke, Database Processing

Functional Dependency (FD) Rules
 If A  (B, C), then A  B and A  C
 If (A,B)  C, then neither A nor B determines C by itself
Kroenke, Database Processing

 A functional dependency is a statement about all allowable instances of a table
 You cannot find the functional dependencies simply by looking at some data:
 Data set limitations
 Must be logically a determinant
 Given some data in a table R, we can check if it violates some FD, but we cannot tell if the FD holds over R!
Kroenke, Database Processing

Functional Dependencies in the
SKU_DATA Table
Assuming data is representative, determine the FD
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Functional Dependencies in the
SKU_DATA Table
SKU  (SKU_Description, Department, Buyer)
SKU_Description  (SKU, Department, Buyer)
Buyer  Department
Kroenke, Database Processing

Class Exercise
Assuming all FD that are verified by the data are indeed FD, determine the FD in the ORDER_ITEM Table
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What Makes Determinant Values Unique?
 A determinant is unique in a relation if, and only if, it determines every other column in the relation
 Unique determinants = superkey
Kroenke, Database Processing

 A set of columns is a key for a relation if :
1. No two distinct rows can have same values in all key columns, and
2. This is not true for any subset of the key
 Part 2 false? A superkey
 Primary key
 Alternate key
Kroenke, Database Processing

 Relations are categorized as a normal form based on which modification anomalies or other problems that they are subject to:
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 Boyce-Codd Normal Form (BCNF) – A relation is in BCNF if every determinant is a candidate key
“I swear to construct my tables so that all nonkey columns are dependent on the key, the whole key and nothing but the key, so help me Codd.”
Kroenke, Database Processing

Eliminating Modification Anomalies from
Functional Dependencies in Relations
 Put all relations into Boyce-Codd Normal Form
(BCNF):
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Putting a Relation into BCNF:
EQUIPMENT_REPAIR
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Putting a Relation into BCNF:
EQUIPMENT_REPAIR
EQUIPMENT_REPAIR (ItemNumber, Type, AcquisitionCost,
RepairNumber, RepairDate, RepairAmount)
ItemNumber  (Type, AcquisitionCost)
RepairNumber  (ItemNumber, Type, AcquisitionCost,
RepairDate, RepairAmount)
ITEM (ItemNumber, Type, AcquisitionCost)
REPAIR (ItemNumber, RepairNumber, RepairDate, RepairAmount)
Where REPAIR.ItemNumber must exist in
ITEM.ItemNumber
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Putting a Relation into BCNF:
New Relations
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Class Exercise
Put the following relation into BCNF
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 A multivalued dependency occurs when a determinant determines a particular set of values:
Employee  Degree
Employee  Sibling
PartKit  Part
 The determinant of a multivalued dependency can never be a primary key
Kroenke, Database Processing

Kroenke, Database Processing

Eliminating Anomolies from
Multivaled Dependencies
 Multivalued dependencies are not a problem if they are in a separate relation, so:
 Always put multivalued dependencies into their own relation
 This is known as Fourth Normal Form (4NF)
Kroenke, Database Processing