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This page is for anyone using an ERD to define a data structure. It explains the properties for relationships. 

Overview

Example

The following is an ERD diagram for a school which consists of 6 entities, which are represented by the 6 tables interlinked by Relationships: 


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  1. SchoolDept, a simple table that obtains much of its key information from the ClassRoom and Teacher tables. This information is available my means of relationships with these two tables. This avoids the need to store any duplicate information against the School Department. UID is the Primary Key and Name is the Display Name.
  2. ClassRoom, details of the class room, with additional information provided by the SchoolDept.
  3. Course, details the courses. It has a relationship to Teacher and CourseAttendee which provide their respective details. 
  4. Student, details all the information about a student. The courses they attend are held in the CourseAttendee table with the information being made available by the relationship between the aforementioned. 
  5. CourseAttendee, details the attendees of each course. this is a special table that has been configured to support a many to many relationship between the Course and the Students.