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#1 Matty919  Icon User is offline

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ER Diagram Questions

Posted 08 December 2011 - 09:31 AM

Some questions about ER diagrams:

Question 1:

In Chen ER diagrams do you list attributes that are just there to create relationships i.e. foreign keys?

So for example if you have car and owner entities where a car can only have one entity.

Owner(OwnerID, Name, DOB)
Car(CarID, Name, OwnerID)

Would the bolded attribute be correct?

Question 2:

If a linking table has 3 attributes e.g. E.g. a school course has modules which are optional or compulsory. This would be a many to many relationship. How would the compulsory or optional aspect be implemented:

CourseModuleLink(CourseID, ModuleID, Compulsory)

Where compulsory could be Y/N. What would be the best way to show this on an ER diagram using Chen? Just have text for the relationship with the words: Course "contains optional or compulsory" modules

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