ERD IN CLASS EXAMPLES - DePaul University
ERD IN CLASS EXAMPLES
Business rules (i.e., relationships)
Example 1
1. a professor teaches zero, one or many classes and a class is taught by one professor
2. a course may generate zero, one or many classes and a class comes from one course
3. a class is held in one room but a room has many classes
Example 2 (try this at home and if you have questions raise them next class)
1. an invoice is written by one salesrep but a salesrep writes many invoices
2. a vendor sells many products but a product is bought from one vendor
3. an invoice has one or many products and a product is found on zero, one or many invoices
Example-1 Solution (Incomplete)
The many-to-many relationship is not resolved, therefore the solution is incomplete. In the final solution the many-to-many must always be resolved.
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Final Solution (Complete)
In this example, the many-to-many relationship between student and class is resolved.
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Solution to the INVOICE problem
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