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Lecture 4

• Normalization

• An Normalization example

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Normalization

A process for evaluating and correcting table structure

Minimize data redundancy

Eliminate Anomalies

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Is Normalization Necessary?

NO

But it is helpful to maintain data integrity and consistency

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Denormalization

• Reversing normalization

• i.e from 3rd NF to 2nd NF

• Or 2nd to 1st NF

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Anomalies

• Update—requires update in multiple locations

• Deletion—A deletion may lose important information

• Insertion—Requires complete definitions, ie does see page 187 (an employee can not be entered unless he is assigned a project

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Normalization Process

• 1st NF

• 2nd NF

• 3rd NF

• Almost for 90-98% application 3rd NF is sufficient

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Dependency

When an attribute value depends on attribute B then B is dependent on A

A---B

or values of B can be determined by value of A, reverse may or may not be true

Ex:

ssn--Name

SSN, CID--Grade

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Un-normalized relation

Remove REPEATING groups1st NF

Remove PARTIAL dependency

2nd NF

Remove TRANSIENT dependency

3rd NF Every determinant is a candidate key

Boyce-CODD NF

If we can convert a relation into 3NF almost 90-98% of anomalies are removed

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Un-normalized formA relation is in un-normalized form, if it contains repeating groupTypically shown in parentheses

Ex: PART NO   DESC.     VENDOR-NAME   ADDRESS  UNIT-COST

 1234            LOGIC INTEL                   SAN JOSE    150.00                      chip           LSI LOGIC            SAN JOSE    120.00

 5678     MEMORY   INTEL                  SAN JOSE     50.00 chip

SUPPLIER (Part_no, Part_DESC, (Vendor_name, Vendor_address, Unit_cost))

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Another Way

(Part_NO, V_NAME)-> Unit_cost

Part_NO->P_Desc (Partial dependency)

V-Name->V_DESC (Partial Dependency)

Part_NO P-DESC V_NAME V_ADDRESS UNIT_COST

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1st NFA relation is in 1st NF if it does NOT contain any repeating groups(Part_no, Part_DESC, (Vendor_name, Vendor_address, Unit_cost))

1st NF..remove repeating groupsBreak it into TWO relations

One without repeating group and ONE with repeating group AND PK of other relation

S1 (Part_no, Part_DESC)S2 (Vendor_name, Part_no, Vendor_address, Unit_cost

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2nd NF

A relation is in 2nf NF if it is in 1stNF and it does not contain any partial dependency

Partial dependency: A partial dependency exists if an attribute is dependent ONLY on PART of the PK and the WHOLE PK

We must examine each relation for partial dependency

NOTE: A partial dependency can only exist if there are more than ONE attribute as PK

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S1 (Part_no, Part_DESC)S2 (Vendor_name, Part_no, Vendor_address,

Unit_costNote S1 is already in 2nd NF since there is only

attribute as PKIn S2:Question is Vendor_address dependent on BOTH

vendor_name AND Part_NO?

Question is Unit_price dependent on BOTH vendor_name AND Part_NO?

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Question is Vendor_address dependent on BOTH vendor_name AND Part_NO?

Answer: NO

Give me vendor_no and I can find vendor_address, we do NOT need Part_No to know vendor_address, ie Vendor_address depends ONLY Vendor_name, hence the partial dependency

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Question is Unit_price dependent on BOTH vendor_name AND Part_NO?

YES if you examine the table, price changes with vendor and part_no, ie price depnds on both Part_no AND which vendor supplies it

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Remove Partial Dependency

VENDOR _ADDRESS

VENDOR_name

UNIT_PRICE

PART#

Create TWO tables:

One with Partial dependency and other without it

S21 (Vendor_name, vendor_address)

S22(Vendor_name, Part_no, Unit_price)

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3rd NF

A relation is in 3rd NF if it is in 2nd NF and it does not contain any transitive dependency

Transitive dependency: A transitive dependency exists when some of the non-key attributes are dependent on other non-key attributes

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So far we have three relations that are in at least 2nd NF

S1 (Part_no, Part_DESC)S21 (Vendor_name, vendor_address)S22(Vendor_name, Part_no, Unit_price)

S1, S21 & S22 are also in 3rd NF since there is ONLY ONE non_key attribute and transitive dependency can NOT exist

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ERD

PART PART-SUPPLIED VENDOR

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Q6/p 175

A Using notation from the booka. (C1, C3)- C2,C4,C5(i.e., C2, C4, C5) are functionally dependent on C1 and C3Above relation is in at least 1stNF, since there are No

repeating groups

C1C2 there is PARTIAL dependency since C2 depends on PART of the PK and the whole PK

C4--C5 (transitive dependency since C5 ( a non-PK attribute) depends on another non-PK attribute (C4)

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Part b

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Part c

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Q8/P177

Table P5.8 Sample ITEM Records

Attribute NameSample Value Sample Value Sample Value

ITEM_ID 231134-678 342245-225 254668-449

ITEM_LABEL HP DeskJet 895Cse HP Toner DT Scanner

ROOM_NUMBER 325 325 123

BLDG_CODE NTC NTC CSF

BLDG_NAME Nottooclear Nottoclear Canseefar

BLDG_MANAGER I. B. Rightonit I. B. Rightonit May B. Next

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ITEM_DESCRIPTION BLDG_CODE BLDG_NAME BLDG_MANAGERITEM_ID BLDG_ROOM

Problem 8 Solution

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ITEM_DESCRIPTION BLDG_CODE

BLDG_NAME

EMP_FNAME EMP_INITIAL

BLDG_NAME BLDG_MANAGER

BLDG_CODE

EMP_CODE EMP_LNAME

Problem 9 Solution: All tables in 3NF

ITEM_ID BLDG_ROOM

ITEM_DESCRIPTIONITEM_ID BLDG_ROOM BLDG_CODE

EMP_CODE

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