Database Chapter02-02

8/10/2019 Database Chapter02-02

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CHAPTER 2

DATABASE DESIGN

1

Database Application

SAK 3408


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Learning Objectives (W3)2

Describe the database design phases.

Explain on how to construct E-R diagram.

Transform ERD into Relation.

Use normalization to decompose a relationwith anomalies into well-structured relations.


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Relation3

Definition: A relation is a named, two-dimensionaltable of data

Table is made up of rows (records), and columns (attribute orfield)

Not all tables qualify as relations Requirements:

Every relation has a unique name.

Every attribute value is atomic (not multivalued, notcomposite)

Every row is unique (cant have two rows with exactly thesame values for all their fields)

Attributes (columns) in tables have unique names

The order of the columns is irrelevant

The order of the rows is irrelevant


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What is atomic value?4

OrderID CustID Date Items

1 4 4/11/02 5 Pencils, 3 Erasers, 6 Rulers

2 23 6/11/02 1 Scissor

3 15 7/11/02 2 Pen, 2 Notebook

4 2 7/11/02 15 5" Magazine File

5 23 7/11/02 1 Stapler

6 2 8/11/02 5 Kingston USB Flash Drive 8GB

This mean that in your table, for every row-by-column

position (cell), there exists only one value - not an

array or list of values:


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Is this a relation?5

OrderID CustID Date Quantity Items

1 4 4/11/02 5 Pencils

1 4 4/11/02 3 Erasers

1 4 4/11/02 6 Rulers

2 23 6/11/02 1 Scissor

3 15 7/11/02 2 Pen

3 15 7/11/02 2 Notebook

4 2 7/11/02 15 5" Magazine File

5 23 7/11/02 1 Stapler

6 2 8/11/02 5 Kingston USB Flash Drive 8GB


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Transforming E-R into Relations10

Step 1: Mapping Regular Entities to Relations

1. Simple attributes: E-R attributes map directly onto

the relation

2. Composite attributes: Use only their simple,

component attributes

3. Multi-valued Attribute - Becomes a separate

relation with a foreign key taken from the superiorentity


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(a) CUSTOMER entity

type with simpleattributes

Figure 2.12 Mapping a regular entity

(b) CUSTOMER relation


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(a) CUSTOMER entity

type with composite

attribute

Figure 2.13 Mapping a composite attribute

(b) CUSTOMER relation with address detail


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Figure 2.14 Mapping a multivalued attribute

1 to many relationship between original entity and new relation

(a)

Multivalued attribute becomes a separate relation with foreign key

(b)


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Step 2: Mapping Weak Entities

Becomes a separate relation with a

foreign key taken from the superiorentity

Primary key composed of:

Partial identifier of weak entityPrimary key of identifying relation (strong

entity)


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Figure 2.15 Mapping a weak entity

(a) Weak entity DEPENDENT


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Step 3: Mapping Binary

Relationships

One-to-Many - Primary key on the one sidebecomes a foreign key on the many side

Many-to-Many - Create a new relationwith the

primary keys of the two entities as its primary

keyOne-to-One - Primary key on the mandatory

side becomes a foreign key on the optional

side


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Figure 2.16 mapping a 1:M relationship

(a) Relationship between customers and orders


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(b) Mapping the relationship

Again, no null value in theforeign keythis is

because of the mandatory

minimum cardinality

Foreign key


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Figure 2.17 Mapping M:N relationship

(a) ER diagram (M:N)

The Suppliesrelationship will need to become a separate relation


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(b) Three resulting relations

Newintersection

relationForeign key

Foreign key

Composite primary key


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Figure 2.18 Mapping a binary 1:1 relationship

(a) Binary 1:1 relationship


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Step 4: Mapping Associative Entities

Identifier Not Assigned

Default primary key for the association relation is

composed of the primary keys of the two entities (as inM:N relationship)

Identifier Assigned

It is natural and familiar to end-users

Default identifier may not be unique


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Figure 2.19 Mapping an associative entity

(a) Associative entity


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(b) Three resulting relations


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Figure 2.20 Mapping a unary 1:N relationship

(a) EMPLOYEE entity

with Manages

relationship

(b) EMPLOYEE

relation with

recursive foreign

key


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29

Mapping a unary M:N relationship

(a) Bill-of-materials

relationships (M:N)

(b) ITEM andCOMPONENT

relations


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Step 6: Mapping Ternary (and n-ary)

Relationships

One relation for each entity and one for theassociative entity

Associative entity has foreign keys to each

entity in the relationship


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Figure 2.21 Mapping a ternary relationship

(a) Ternary relationship with associative entity


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(b) Mapping the ternary relationship

Remember that the primary

key MUST be unique


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Step 7: Mapping Supertype/Subtype

Relationships One relation for supertype and for each subtype

Supertype attributes (including identifier and subtype

discriminator) go into supertype relation

Subtype attributes go into each subtype; primary key of

supertype relation also becomes primary key of subtype

relation

1:1 relationship established between supertype and

each subtype, with supertype as primary table


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Figure 2.22 Supertype/subtype relationships

(a)


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Exercise (1)36

phone


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Exercise (2)37


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Exercise (3)38


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Exercise (4)39


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Exercise (5)40


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Exercise (6)

Game

Name Graphics Sound

Gameplay Platform

Developer

Name

Phone no

Rater

Name

Ability

rates by

41


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Exercise (7)42

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