DATABASE SYSTEMS
13th Edition
ISBN: 9780357095607
Author: Coronel
Publisher: CENGAGE L
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Chapter 4, Problem 1RQ
Explanation of Solution
Conditions:
Following are the conditions should be met before an entity is referred as a weak entity:
- The entity should be “existence-dependent” on its parent entity.
- If an entity is referred as an “existence-dependent”, then that entity can exist in the
database if and only if when it is related with another entity existence.
- If an entity is referred as an “existence-dependent”, then that entity can exist in the
- The entity should inherits a section of its primary key (PK) from its parent entity.
Example:
Consider the following ER diagram along with its attributes:
Explanation:
- The entity CLASS is “existence-dependent” on COURSE entity. Hence the CLASS entity uses a PK component from its parent entity (COURSE).
- The CLASS entity’s PK is (COURSE_ID, CLASS_SEC).
- In this strong implementation, the CLASS entity is referred as a weak entity between COURSE and CLASS.
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Write a program that simulates a Magic 8 Ball, which is a fortune-telling toy that displays a random response to a yes or no question. In the student sample programs for this book, you will find a text file named 8_ball_responses.txt. The file contains 12 responses, such as “I don’t think so”, “Yes, of course!”, “I’m not sure”, and so forth. The program should read the responses from the file into a list. It should prompt the user to ask a question, then display one of the responses, randomly selected from the list. The program should repeat until the user is ready to quit.
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Chapter 4 Solutions
DATABASE SYSTEMS
Ch. 4 - Prob. 1RQCh. 4 - What is a strong (or identifying) relationship,...Ch. 4 - Prob. 4RQCh. 4 - Suppose you are working within the framework of...Ch. 4 - Prob. 6RQCh. 4 - Prob. 7RQCh. 4 - Discuss the difference between a composite key and...Ch. 4 - What two courses of action are available to a...Ch. 4 - What is a derived attribute? Give an example. What...Ch. 4 - Prob. 11RQ
Ch. 4 - Discuss two ways in which the 1:M relationship...Ch. 4 - Prob. 13RQCh. 4 - Prob. 14RQCh. 4 - Briefly, but precisely, explain the difference...Ch. 4 - What are multivalued attributes, and how can they...Ch. 4 - Prob. 17RQCh. 4 - Prob. 18RQCh. 4 - What two attributes must be contained in the...Ch. 4 - Describe precisely the composition of the...Ch. 4 - Prob. 21RQCh. 4 - Prob. 1PCh. 4 - Create a complete ERD in Crows Foot notation that...Ch. 4 - Prob. 4PCh. 4 - Prob. 5PCh. 4 - Prob. 6PCh. 4 - Prob. 7PCh. 4 - Prob. 8PCh. 4 - Prob. 9PCh. 4 - Prob. 10PCh. 4 - Prob. 11C
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