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.

1. A company operates many departments.
2. Each department employs one or more employees.
3. Each of the employees might or might not have one or more dependents.
4. Each employee might or might not have an employment history.

 

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