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tloi
Posts: 16
Posted 12:26 Apr 18, 2012 |

I have questions related to subclass. Is "isa" have similarity to 'one-to-many' relationships?
Second, can a subclass entity set had relationships like others entity set in ER Diagram?
Is the key  of subclass entity set have only the key from its superclass?

cysun
Posts: 2935
Posted 12:32 Apr 18, 2012 |

1. No, "isa" is not a relationship.

2. Yes.

3. Yes. If a subclass has a different key than the super class, it shouldn't be a subclass.