Generalization/realization

General Questions/Discussions
1

Hi,

How do I create generalization on ERD model. for exampe I have Entity Test which has 2 sub entities open test and close test.

Tnx,

or

2

Hi user,

Thanks for your post. I don’t think Generalization is a native concept in ER model, and database management system (DBMS) does not offer a way to enforce that kind of relationship. I think this is more an Object-Oriented concept.

But if you want to implement it in a database, you can still create Test and columns on it to store general information for a test. Then create OpenTest and CloseTest and create columns on them to store specific information of open/close test.
But this kind of relations cannot be completely enforced by the DBMS. At most you can define foreign keys to ensure that every open and close test exist in the main test table.

Hope this helps. Please do not hesitate to ask if there is any further question.

Best regards,
Lilian Wong