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Relational Database and Normalization

Entity-Relationship Model. RelationshipsEntity-Relationship Model. Relationships

Relationship

Relational databases have various relationships that can be depicted on diagrams.

There are different dependencies between entities, and each defines the interaction between a number of elements. An element can interact with several or only one, which is referred to as a relationship.

Relational databases have various relationships that can be depicted on diagrams.

Types of relationships:

  • One-to-One
  • One-to-Many
  • Many-to-One
  • Many-to-Many

The various relationship types will be discussed in detail later, but here is a representation of the different relationship types:

Mandatory and optional relationships

Mandatory and optional relationships are represented with additional marks as | (line) and o (circle), respectively.

  • A mandatory relationship means that an instance of one entity must be related to another entity.
  • An optional relationship indicates that any instance of one entity can be related to another entity, but it is not required to do so.

Look at the examples:

Mandatory and optional relationships are used infrequently, but it is essential to know these marks.

1. Select all relationship types:
2. Choose marks:

question-icon

Select all relationship types:

Select a few correct answers

question-icon

Choose marks:

The mandatory mark is
_ _ _
.

The optional mark is
_ _ _
.

Click or drag`n`drop items and fill in the blanks

dots
| (line)
dots
o (circle)

Section 1.

Chapter 4