1. What is an associative entity? When must a many-to-many relationship be modelled as an associative entity? Provide some examples demonstrate this issue.
2. Draw an ERD for an eyeglass store database with the following information:
a. Customers have prescriptions from eye doctors.
b. Customers buy frames that come from manufacturers
c. Customers are helped by a staff member
3. Draw seven E-R diagrams for seven different types of relationships as follows:
a. One to one relationship
b. One to many relationship
c. One to one or many relationship
d. One to one or zero relationship
e. One or many to one or many relationship
f. Many to many relationship
g. Zero or one to many relationship
In each E-R diagram, write two sentences (a) as you read from left to right and (b) as you read from right to left.
2. Draw an ERD for an eyeglass store database with the following information:
a. Customers have prescriptions from eye doctors.
b. Customers buy frames that come from manufacturers
c. Customers are helped by a staff member
3. Draw seven E-R diagrams for seven different types of relationships as follows:
a. One to one relationship
b. One to many relationship
c. One to one or many relationship
d. One to one or zero relationship
e. One or many to one or many relationship
f. Many to many relationship
g. Zero or one to many relationship
In each E-R diagram, write two sentences (a) as you read from left to right and (b) as you read from right to left.