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Database Systems: Design, Implemen...

13th Edition
Carlos Coronel + 1 other
Publisher: Cengage Learning
ISBN: 9781337627900

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BuyFindarrow_forward

Database Systems: Design, Implemen...

13th Edition
Carlos Coronel + 1 other
Publisher: Cengage Learning
ISBN: 9781337627900
Chapter 4, Problem 11RQ
Textbook Problem
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How is a relationship between entities indicated in an ERD? Give an example using the Crow’s Foot notation.

Program Plan Intro

Entity:

In ER model, the term “entity” refers to the actual entity set. It is represented by a rectangle box which contains the entity name.

  • There is no any difference among various types of entities such as a weak entity and a composite entity. But Crows Foot use different relation types as strong or weak.
  • A composite entity is stated that one or more PK attributes is also a Foreign Key (FK).

Explanation of Solution

Entity relationship in ERD:

The relationship strength is based on how the Primary Key (PK) of an associated entity is stated or defined. The types of relations are:

  • A weak relationship
  • A strong relationship

Weak relationship:

A weak relationship may exist when the Primary Key (PK) of the associated entity does not include more than one of the PK attributes of the parent entity.

  • In Crow’s Foot ERD notation, a weak relationship is described using a “dashed line” among the entities.

Example:

Consider the below ER diagram illustrate the Crow’s Foot notation for a weak relationship:

Explanation:

  • The COURSE entity’s PK had included as Foreign Key (FK) in the CLASS entity. Hence the COURSE_ID has been serving as FK to COURSE entity.
  • In Crow’s Foot, a weak relationship is illustrated using “dashed line” among entities.

Strong relationship:

A strong relationship will occurs when an entity is existence-dependent on other entity and inherits more than one part of its Primary Key (PK) from that entity...

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