Review Questions: What two conditions must be met before an entity can be classified as a weak
Question:
Review Questions:
What two conditions must be met before an entity can be classified as a weak entity? Give an example of a weak entity.
What is a strong (or identifying) relationship, and how is it depicted in a Crow’s Foot ERD?
Given the business rule “an employee may have many degrees,” discuss its effect on attributes, entities, and relationships. (Hint: Remember what a multivalued attribute is and how it might be implemented.)
What is a composite entity, and when is it used?
Suppose you are working within the framework of the conceptual model in Figure Q4.5.
Figure Q4.5 The Conceptual Model for Question 5
Given the conceptual model in Figure Q4.5, answer the following:
Write the business rules that are reflected in it.
How would you (graphically) identify each of the following ERM components in a Crow’s Foot model?
- An entity
- The multiplicity (0:M)
- A week entity
- a strong relationship
Discuss the difference between a composite key and a composite attribute. How would each be indicated in an ERD?
What is a derived attribute? Give an example.
PROBLEMS
1. Given the following business rules, create the appropriate Crow’s Foot ERD.
- A company operates many departments.
- Each department employs one or more employees.
- Each of the employees might or might not have one or more dependents.
- Each employee might or might not have an employment history.
Database Systems Design Implementation and Management
ISBN: 978-1285196145
11th edition
Authors: Carlos Coronel, Steven Morris