Hello

Let me start by saying that I'm new in the database world. So now that
you know, here is my problem :-)

I have multiple "items" that share several attributes. So being a
OO-programmer, I instantly think of a class hierarchy. Having a
abstract base class with the common attributes, and then multiple
entity classes inheriting from the abstract base class, and adding
their specific attributes.

But how do I implement such a relationship in Firebird. Here is my idea:

Item table:
ID (PK) (auto incremented)
ItemType (FK or domain, more on that later)
The common attributes

Book table:
ID (PK) (same ID as in item table, so not auto incremented)
The book specific attributes

CD table:
ID (PK) (same ID as in item table, so not auto incremented)
The cd specific attributes


Is that a good generalization design?


About the ItemType column. I see two ways to implement this

1)
Use a ItemType table:
ID int (ID, is going to be foreign key in Item table)
Type string (would be "book" or "cd")

2)
Another way would be using a Domain, it seems easier.
But is domain good practice?
If I in the future would move to another database, would using domain
give me trouble?

Thanks a lot