Chapter 4 The Relational Model and Normalization

Chapter 4The Relational Model and

Normalization

Database Processing: Fundamentals, Design and Implementation, 9/e by David M. Kroenke

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Relations Relational DBMS products store data in the form of relations, a special

type of table A relation is a two-dimensional table that has the following

characteristics• Rows contain data about an entity• Columns contain data about attributes of the entity• All entries in a column are of the same kind• Each column has a unique name• Cells of the table hold a single value• The order of the columns is unimportant• The order of the rows is unimportant• No two rows may be identical

Although not all tables are relations, the terms table and relation are normally used interchangeably• Table/row/column = file/record/field = relation/tuple/attribute


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Example: Relation


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Example: Tables Not Relations


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Functional Dependencies A functional dependency occurs when the value of one (set

of) attribute(s) determines the value of a second (set of) attribute(s)

The attribute on the left side of the functional dependency is called the determinant• SID GPA• SKU Department, SKU_Description• (CustomerNumber, ItemNumber, Quantity) Price

Mathematically, we say that “A” determines “B”, A B – Physically, we might say that “A” is a unique identifier for

“B”


Functional Dependency (2)

Full Functional Dependency: “B” is functionally dependent on “A” but not on any subset of “A”

• Transitive Dependency: If “B” and “C” are both dependent on “A”, but “C” is also dependent on “B”, we say that “C” is transitively dependent on “B”

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Normalization

Normalization eliminates modification anomalies• Deletion anomaly: deletion of a row loses information

about two or more entities• Insertion anomaly: insertion of a fact in one entity

cannot be done until a fact about another entity is added Anomalies can be removed by splitting the relation

into two or more relations; each with a different, single theme

Normalization works through classes of relations called normal forms


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Relationship of Normal Forms


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Normal Forms Any table of data is in 1NF if it meets the

definition of a relation A relation is in 2NF if all its non-key attributes are

dependent on all of the key (no partial dependencies)• If a relation has a single attribute key, it is

automatically in 2NF A relation is in 3NF if it is in 2NF and has no

transitive dependencies A relation is in BCNF if every determinant is a

candidate key A relation is in fourth normal form if it is in BCNF

and has no multi-value dependencies


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Example: 2NF


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Example: NOT IN 3NF


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Example: 3NF


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Example: NOT IN BCNF


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Example: BCNF


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Another Example: NOT IN BCNF

CUSTOMER ID Tool Type Tool trainer ID

CUSTOMER ID + Tool Type Tool Trainer IDCUSTOMER ID + Tool TRAINER ID is also an candidate key (unique)Tool TRAINER ID Tool Type

Specialized tool maker

CUSTOMER ID Tool trainer ID Tool Type Tool trainer ID


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Example: NOT IN 4NF


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Example: 4NF


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Example: 4NFCUSTOMER ID Tool Types Favorite Sports

CUSTOMER ID Tool Types

CUSTOMER ID Favorite Sports


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DK/NF

First published in 1981 by Fagin DK/NF has no modification anomalies;

so no higher normal form is needed A relation is in DK/NF if every constraint on the

relation is a logical consequence of the definition of keys and domains


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Example 1: DK/NF


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Example: DK/NF


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Normal Forms-Review Any table of data is in 1NF if it meets the

definition of a relation A relation is in 2NF if all its non-key attributes are

dependent on all of the key (no partial dependencies)• If a relation has a single attribute key, it is

automatically in 2NF A relation is in 3NF if it is in 2NF and has no

transitive dependencies A relation is in BCNF if every determinant is a

candidate key A relation is in fourth normal form if it is in BCNF

and has no multi-value dependencies


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De-normalized Designs When a normalized design is unnatural, awkward,

or results in unacceptable performance, a de-normalized design is preferred

Example • Normalized relation

CUSTOMER (CustNumber, CustName, Zip) CODES (Zip, City, State)

• De-Normalized relations CUSTOMER (CustNumber, CustName, City, State, Zip)

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Chapter 4 The Relational Model and Normalization