Tutorial :Is there a way to specify a super-type sub-type relationship in Oracle Designer?



Question:

I was wondering if it is possible to create a super-type sub-type relationship in Oracle Designer. I would like to create something like this:

alt text http://ww2.cis.temple.edu/cis109friedman/CIS%20109%20-%20Lecture%20Set%20III%20-%20ERD%20and%20EERDs%20and%20Modeling/Emp-super.gif

Thanks.


Solution:1

In entity relationship diagrams subtypes are created by creating a new entity inside an existing entity like this example from InformIT.com:

ERD Diagram http://www.informit.com/content/images/chap3_0130282286/elementLinks/03fig28.gif

This shows that ORDER has subtypes PURCHASE ORDER and SALES ORDER, i.e. every ORDER is either a PURCHASE ORDER or a SALES ORDER.

Subtypes can be nested to any depth.

Although this example doesn't show any, subtypes can also have their own attributes and relationships.


Solution:2

Note that if you're working in the Design Editor on the physical model, you have to implement as actual tables.

But take a look at the documentation for the Foreign Key property "Arc", which might help some. You can set it so that exactly 1 of several foreign keys can have a value.

For example, you might set up FK's from your supertype table to each subtype table. Then enforce that exactly one can have a value by using that property and generating the TAPI for the tables. (The drawback is that you'd have to insert the subtype information before the supertype.)


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