Normalization
ISYS 464
Database Design Based on ERD
• Strong entity: Create a table that includes all simple attributes
– Composite
• Weak entity: add owner primary key
• Multi-valued attribute: Create a table for each multi-valued
attribute
– Key + attribute
• Relationship:
– 1:1, 1:M
• Relationship table: for partial participation to avoid null
• Foreign key
– M:M: relationship table
– N-ary relationship: relationship table
– Recursive relationship
• Attribute of relationship
• Superclass and subclass
• Note: The database designed according to these
rules will meet the 3NF requirements.
Database design objectives
• Eliminate data duplication.
• Link related records in related tables.
Example
Employee/Dependent report:
EmpID: E101
Ename: Peter
Address: 123 XYZ St
DependentName
Relationship DOB
Nancy
Daughter
1/1/95
Alan
Son
12/25/03
EmpDependent Table:
EmpID EmpName Address DepName Relation DepDOB
E101 Peter
123 XYZ St Nancy
D
1/1/95
E101 Peter
123 XYZ St Alan
S
12/25/03
Note: This database is able to produce the report, but has
duplicated data.
Update Anomalies Due To
Duplication
• Modification anomaly:
– Inconsistent data
• Insertion Anomalies:
– Enter an employee with no dependent
– Null
• Deletion Anomaly:
– If Nancy and Alan become independent.
If we mix multivalue attribute with
regular attributes in one table
• Employee Table:
– SSN, Ename, Sex, DOB, Phone
– Employee may have more than 1 phone.
• Key: SSN or SSN + Phone
• Duplication ?
Example 2
• EmpDependent table:
– EmpID, Ename, Address, Depname, Relation,
DepDOB
• Key: EmpID + Depname
If we mix two entities with 1:M relationship
in one table
• FacultyStudent table:
– Faculty Advise Student: 1:M relationship
– FID, Fname, SID, Sname, SAddress
• Key: SID
• Duplication?
If we mix two entities with M:M
relationship in one table
• StudentCourse table:
– SID, Sname, GPA, CID, Cname, Units
• Key: SID + CID
• Duplication?
Normalization
• Decompose unsatisfactory relation into smaller
relations with desirable properties.
– No duplication
• The original relation can be recovered by applying
natural join to the smaller relations.
– So that no information is lost in the process.
• Keys and function dependency:
– Which field is the key field of the EMpDependent
Table?
• EmpID + DepName
Function Dependency
• Relationship between attributes
• X -> Y
– The value of X uniquely determines the value
of Y.
– Y is functionally dependent on X.
– A value of X is associated with only one value
of Y.
Example
• Employee table:
–
–
–
–
SSN
S1
S2
S3
Ename
Peter
Paul
Mary
Sex
M
M
F
DOB
1/1/75
12/25/80
7/4/72
• Function Dependencies:
– SSN -> Ename, SSN ->Sex, SSN -> DOB
– SSN -> Ename, Sex, DOB
• Any other FD:
– Ename -> SSN ?
– Ename -> Sex ?
– DOB -> SSN ?
• What is the key of Employee table:
– SSN
• Observations:
–
–
–
–
All non-key fields are functionally dependent on SSN.
There is no other FD.
The only FD is the key dependency.
There is no data duplication in the Employee table.
Normalization Process
• Inputs:
– A “universal relation”
– Function dependencies
• Output: Normalized tables
• Process:
– Decompose the unnormalized relation into smaller
relations such that in each relation the non key fields
are functionally dependent on the key, the whole key,
and nothing but the key. So help me Codd!
First Normal Form
• The fields of a relation are all simple
attribute.
– All relational database tables meet this
requirement.
• EmpDependent table:
– EmpID, Ename, Address, Depname, Relation, DepDOB
– First normal form? Yes
– Second normal form?
Second Normal Form
• The non-key fields are functionally
dependent on the key, and the whole key.
– FD:
• EmpID ->Ename, Address
– Key: EmpID + Depname
– Ename and Address depend on part of the key.
• Every non-key field is fully functionally dependent on the
key.
• Decompose the EMpDependent table into two tables:
– EmpID, Ename, Address
– EmpID, Depname, Relation, DepDOB
• Employee Table:
– SSN, Ename, Sex, DOB, Phone
– Employee may have more than 1 phone.
• FD:
– SSN -> Ename, Sex, DOB,
– SSN -> Phone ?
• Key: SSN + Phone
• 2NF? No
• Decompose into two tables:
– SSN, Ename, Sex, DOB
– SSN, Phone
• FacultyStudent table:
– Faculty Advise Student: 1:M relationship
– FID, Fname, Office, SID, Sname, SAddress
• FD:
– FID -> Fname, Office
– SID -> Sname, SAddress, FID, Fname, Office
•
•
•
•
Key: SID
2NF ? Yes
Duplication? Yes
Why?
– All non-key fields depend on the whole key, but not Nothing But
the Key!
• SID -> FID, Fname, Office
• FID -> Fname, Office
Transitive Dependency
• If X -> Y, and Y->Z then X -> Z.
• Z if transitively dependent on the key.
• SID -> FID, FID -> Fname, Office
– SID -> Fname, Office
– Fname and Office are transitively dependent on
SID.
Third Normal Form
• Every non-key field is:
– Fully functionally dependent on the key, and
– Non-transitively dependent on the key.
• Decompose:
– FID, Fname, Office
– SID, FID, Sname, SAddress
Example
Customer/Orders report:
CID: C101
Cname: Peter
Address: 123 XYZ St
OID
Odate
SalesPerson
Amount
O25
1/1/04
John
125
O30
2/25/04
Alan
500
CustomerOrders Table:
CID
CName Address
C101 Peter 123 XYZ St
C101 Peter 123 XYZ St
OID
Odate SalesPerson Amount
O25
1/1/04
John
125
O30
2/25/04 Alan
500
Example
• Key: OID
• FD:
– OID -> CID, Cname, Address, Odate, SalesPerson, Amount
– CID -> Cname, Address
• 2NF? Yes
• 3 NF? No
• Decompose:
– CID, Cname, Address
– OID, CID, Odate, SalesPerson, Amount
Example with 1:M Relationship
• FacultyStudent table:
– Faculty Advise Student: 1:M relationship
– FID, Fname, SID, Sname, SAddress
• FD:
– FID -> Fname
– SID -> Sname, Saddress
•
•
•
•
Key: SID
2NF? Yes
3NF? No, because SID ->FID, FID -> Fname
Decompose:
– Table 1: FID, Fname
– Tablw 2: SID, FID, Sname, SAddress
Example with M:M Relationship
• StudentCourse table:
– SID, Sname, GPA, CID, Cname, Units
• Key: SID + CID
• Function Dependencies:
– SID -> Sname, GPA
– CID -> Cname, Units
• 2NF? No
– Decompose:
• Table 1: SID -> Sname, GPA
• Table 2: CID -> Cname, Units
• Table 3: SID, CID
• 3NF? Yes
Online Shopping Cart
CID
Addr
Cname
Customer
1
Has
CartID
M
Date
ShoppingCart
M
Qty
Has
M
Product
Price
PID
Pname
Normalized Database
• Universal Relation:
– CID, Cname, Addr, CartID, Date, PID, Pname, Price, Qty
• Key: CartID + PID
• FDs:
– CartID -> Date, CID, Cname, Addr
– CID -> Cname, Addr
– PID -> Pname, Price
• Normalized database:
–
–
–
–
CID, Cname, Addr
CartID, Date, CID
PID, Pname, Price
CartID, PID, Qty
Database Design Based on ERD
• Strong entity: Create a table that includes all simple attributes
– Composite
• Weak entity: add owner primary key
• Multi-valued attribute: Create a table for each multi-valued
attribute
– Key + attribute
• Relationship:
– 1:1, 1:M
• Relationship table: for partial participation to avoid null
• Foreign key
– M:M: relationship table
– N-ary relationship: relationship table
– Recursive relationship
• Attribute of relationship
• Superclass and subclass
• Note: The database designed according to these
rules will meet the 3NF requirements.
Denormalization
• The refinement to the relational schema
such that the degree of normalization for a
modified relation is less than the degree of
at least one of the original relations.
• Objective:
– Speed up processing