How is a union different from an inheritence in ER modelling
From: Abhishek <abhisheksgumadi_at_gmail.com>
Date: 15 Feb 2006 06:08:46 -0800
Message-ID: <1140012526.680091.89260_at_g43g2000cwa.googlegroups.com>
Here's a ER modelling situation.
An investor can either be an individual, family or an institution. What I have seen the way it has been modelled is that there are there are three entity types called, INDIVIDUAL, INSTITUTION, FAMILY. Now, a union has been created to show that the union of these three entity types is the INVESTOR enitity type at the bottom. I would like to know how the above implementation is different from the implementation where we can have the INVESTOR as the superclass entity type and then derive three sub classes entity types called INDIVIDUAL, INSTITUTION, FAMILY.
Which one is more advantageous and under what circumstances? Are the above two different implementations the same? Bye Received on Wed Feb 15 2006 - 15:08:46 CET
Date: 15 Feb 2006 06:08:46 -0800
Message-ID: <1140012526.680091.89260_at_g43g2000cwa.googlegroups.com>
Here's a ER modelling situation.
An investor can either be an individual, family or an institution. What I have seen the way it has been modelled is that there are there are three entity types called, INDIVIDUAL, INSTITUTION, FAMILY. Now, a union has been created to show that the union of these three entity types is the INVESTOR enitity type at the bottom. I would like to know how the above implementation is different from the implementation where we can have the INVESTOR as the superclass entity type and then derive three sub classes entity types called INDIVIDUAL, INSTITUTION, FAMILY.
Which one is more advantageous and under what circumstances? Are the above two different implementations the same? Bye Received on Wed Feb 15 2006 - 15:08:46 CET