Comm 226 Assignment 2 ( got 90+) Concordia University
1) Draw the ERD of the database that could be used to support the operations of the business
described in the case (3 marks). The ERD should identify:
•
Primary keys and Foreign keys;
•
Entities and Attributes;
•
Relationships and Cardinalities (e.g. one-to-one, one-to-many).
Next to the ERD in your submission, list the assumptions made when designing the ERD. If an element of
the business case does not provide the information necessary to know for certain whether one design
choice should be made over another, the choice you make will be accepted if it correctly reflects your
assumptions.
SOLUTION TO Q1)
Assumptions:
The relationships are as follows:
1) A book can have been written by many authors and one author can have written many books:
many to many relationships.
2) A customer can buy as many books as they want.
3) Books can be published by only one publisher, but a publisher can publish many books: one to
many relationship
4) A customer can have many orders but only one order can attribute to a single customer: many
to one relationship
5) An order can have multiple books and a book can be part of multiple orders: many to many
relationship
- You cannot have many to many relationships, so transition tables were created to show many
to many relationships between “Book, Author” and “Order and Book” relationship
Assumptions of primary key:
1) Unique
2) Never changing/can’t be repeated
3) Never null
Foreign keys assumptions:
1) Doesn’t have to be unique
2) They can be repeated
3) Multiple foreign keys in one entity
Assumptions on cardinalities (based on what it takes (the minimum) to be in the system or bookstore):
Book and author:
- A book has to be written by a minimum of 1 author (one or many)
- Minimum number of books an author can write is 1 (one or many)
Customer and Books:
- A customer can buy one or more books (one or many)
Book and publisher:
- A book can be published by a minimum of 1 publisher (one or many)
