Database Systems: Design, Implemen...

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



Database Systems: Design, Implemen...

13th Edition
Carlos Coronel + 1 other
Publisher: Cengage Learning
ISBN: 9781337627900
Chapter 4, Problem 11RQ
Textbook Problem

How is a relationship between entities indicated in an ERD? Give an example using the Crow’s Foot notation.

Program Plan Intro


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.


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


  • 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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