Problem 1 Page 45: 1. For each of the following pairs of related entities, indic

Question

Problem 1 Page 45:
1. For each of the following pairs of related entities, indicate whether (under typical circumstances) there is a one-to-many (1:M) or a many-to-many (M:N) relationship. Then, using the shorthand notation introduced in the text, draw a diagram for each of the relationships.
a. STUDENT and COURSE (students register for courses)
b. BOOK and BOOK COPY (books have copies)
c. COURSE and SECTION (courses have sections)
d. SECTION and ROOM (sections are scheduled in rooms)
e. INSTRUCTOR and COURSE

Explanation / Answer

Well think of the entities' relationships this way: 1:M means - For each student they can have multiple courses. M:N means - For each student they can have multiple courses and each course can have multiple students. So, a) M:N since the second statement above is the MOST TRUE. Granted the first one applies as well, the second better describes the relationship. b) 1:M since each book can have any number of copies but one copy of a book can't be linked to multiple books. That is to say a copy of "Harry Potter and the Sorcerer's Stone" can't be linked to any other book other than the original "Harry Potter and the Sorcerer's Stone." c) 1:M for the same reason above. A course has many sections, but each section links back to 1 course. d) 1:M. Each section is assigned a room; however, multiple sections probably wouldn't share a room. If they did then this is M:N. e) 1:M. Each instructor has 1 or more courses. Each course can't have more than one instructor. If it can (hence sections) then this is M:N. I hope this helps.

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