Your unstated business rule is that no employee can have the same address
as a supplier.
My first thought is that the ADDRESS table has a primary key, generated via
a sequence. EMPLOYEE and SUPPLIER each has a foreign key to that primary
key. Do you really care whether an ADDRESS is the address of an employee
or a supplier? Won't you be selecting addresses based on a pre-selected
supplier or employee? All you are concerned with is that each address is
unique.
If that's not true and non-unique addresses are possible and you do care
whether a given address is for an employee or a supplier and you will be
selecting employees and suppliers based on their addresses, then your model
is correct.
"Magaliff,
Bill" To: Multiple recipients of list ORACLE-L
<[EMAIL PROTECTED]>
<Bill.Magalif cc:
f Subject: data modeling question - child
table with multiple parents
@lendware.com
>
Sent by: root
07/31/2002
04:43 PM
Please
respond to
ORACLE-L
Good day, all:
Am curious to hear opinions on how to model a child table that has multiple
parent tables (i.e., foreign key to multiple parents)
Example:
There's a table that stores Addresses (table ADDRESS) for both employees
(table EMPLOYEE) and suppliers (table SUPPLIER).
Each of these tables has a Primary Key field called ID.
One way to set this up would be for the ADDRESS table to have 2 fields,
EMPLOYEE_ID and SUPPLIER_ID, which would be mutually exclusive (i.e., one
or
the other, to indicate the parent record of the address).
Another solutions if for the ADDRESS table to have two fields to indicate
the parent table name and parent table pk value.
The first method enables me (the dba) to create foreign keys from the
address table to each of the parent tables to validate data. The second
method does not enable me to create such foreign keys (leaving it to the
developers to validate date and insure referential integrity) but would
also
easily facilitate the addition of other parent tables (e.g., CONTRACTOR,
VENDOR, etc.) without altering the ADDRESS table itself.
Any and all thoughts, comments, opinions, experiences are most welcome.
Thanks!
bill magaliff
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