Ch 8 - Conceptual Data Modeling

Question 1

What is an ERD conceptual data modeling?

Answer 1

Mainstream approach to conceptual modeling, where entities & relationships are ‘natural’.

Question 2

What is a Entity?

Answer 2

Something of interest in the environment (ie person, place, object, event, concept). represented by a rectangle.

Question 3

What are two specific types of entities?

Answer 3

Strong entity - exists independently
Weak entity - depends on existence of another entity to have significance

Question 4

What is a Relationship?

Answer 4

An association between the instances of one or more entities. We indicate using a diamond. Use double diamond for relationship between weak & strong entity

Question 5

What are Relationship Cardinality types?

Answer 5

Mandatory One - when min & max both = 1
Mandatory Many - when min = 1 & max = many
Optional one - when min = 0 & max = 1
Optional Many - when min = 0 & max = many

Question 6

How are Complex Relationships defined?

Answer 6

All relationships involved are “many to many” and result has independent meaning

Question 7

What are Attributes?

Answer 7

They are properties/charactersitcs of entities; actual data items we collect. Represented by bubble

Question 8

Types of Attributes

Answer 8

Simple (basic level)
Composite (related group of em)
Single-valued (one value per instance)
Multi-value (has multiple values per instance)
Stored (basic)
Dervived (taken/depends on another attribute)