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Example

The following is screenshot shows 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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SchoolDept, a simple table that obtains much of its key information from the

. The diagram has 6 tables, which entities in the school. The tables are linked by lines representing relationships between the data.


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The tables are:

  • SchoolDept is a simple table that defines the UID and Name for departments in the school. UID is the primary key and Name is the display name.
    This table has relationships to 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
  • Because of these relationships, the ClassRoom and Teacher tables can both include a department name, without duplication. UID is the primary key and Name is the Display Name.
  • ClassRoom
, details
  • has details of the class room, with
additional information provided by the
  • the department name provided by SchoolDept.
  • Course
,
  • has details
the
  • of the courses. It
has a relationship to Teacher and CourseAttendee which provide their respective details
  • takes the teachers name from the relationship to Teacher and provides the course name to CourseAttendee. 
  • Student
, details all the
  •  has 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. CourseAttendee, details
  • provides the student's name to CourseAttendee.
  • CourseAttendee has details of 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. 
  • This table takes data from relationships to both Course and Student tables and illustrates a many-to-many relationship between these two tables.