Module 05a - Relationship and Cardinality

Question 1

Data Model vs DB Design

Answer 1

• A data model is a plan or blueprint for a database design
• Data model is more generalized and abstract than DB design
• It is easier to change a data model then it is to change a database design, so it is the place to work through conceptual DB problems.

Question 2

Data Model = Conceptual design

Answer 2

Conceptual design = data model
Logical design
Physical design

Question 3

ER Model

Answer 3

Is a set of concepts and graphical symbols that can be used to create conceptual schemas

Question 4

ER Model versions

Answer 4

• Original ER model - Peter Chen (1976)
• Extended ER model
• Information Engineering (IE) - James Martin (1990) “crow foot notation”
• IDEF1X
• UML

Question 5

Crow foot notation

Answer 5

Developed by James Martin (1990), also known as crow foot notation. It is easier to understand

Question 6

Entity

Answer 6

Something that can be identified and the users want to track

Question 7

Entity class

Answer 7

A collection of entities of a given type

Question 8

Entity instace

Answer 8

The occurrence of a particular entity

Question 9

Attributes

Answer 9

Attributes describe an entity’s characteristics. All entity instances of a given entity class have the same attributes, but vary in the values of those attributes.

Question 10

Identifier

Answer 10

• Are attributes that name, or identify, entity instances.
• The identifier of and entity instance consists of one or more of the entity’s attributes.
• Composite identifiers are identifiers that consists of two or more attributes.
• Identifiers in data models become keys in database designs.

Question 11

Relationships

Answer 11

Associate one entity with another

Question 12

Relationships classes vs Relationships instances

Answer 12

• Relationship classes are associations among entity classes

- Relationships instances are associations among entity instances

Question 13

Degree

Answer 13

Is the number of entity classes in the relationship.

• Two entities have a binary relationship of degree two
• Three entities have ternary relationship of degree three

Question 14

Cardinality

Answer 14

Means “count”, and is expressed as a number.

Question 15

Maximum cardinality

Answer 15

Is the maximum number of entity instances that can participate in a relationship.

Question 16

Minimum cardinality

Answer 16

Is the minimum number of the entity instances that must participate in a relationship.

Question 17

Types of Maximum cardinality

Answer 17

One-to-One [1:1]
One-to-Many [1:N]
Many-to-Many [N:M]

Question 18

HAS-A Relationships

Answer 18

Each entity instance has a relationship with another entity instance.
An EMPLOYEE has one or more COMPUTERs.
A COMPUTER has one assigned EMPLOYEE.

Question 19

HAS-A vs IS-A

Answer 19

Inheritance: IS-A
- Cat “is a” animal

Composition: HAS-A
- Cat “has a” tail

Question 20

Minimum Cardinality values

Answer 20

Minimums are generally stated as either zero or one:
IF zero [0] THEN participation in the relationship by the entity is optional, and no entity instance must participate in the relationship.
IF one [1] THEN participation in the relationship by the entity is mandatory, and at least one entity instance must participate in the relationship.

Question 21

Minimum Cardinality representation

Answer 21

Minimum cardinality of zero [0] indicating optional participation is indicated by placing an oval next to the optional entity.
Minimum cardinality of one [1] indicating mandatory (required) participation is indicated by placing a vertical hash mark next to the required entity.