Although I agree in principle that most common scenario regarding phone numbers is that there is one per person, in the system that I am designing that is just not the case. The [Phone] table stores office, home, mobile, mobile2, fax numbers for the majority of parent objects, but not all as some could have no phone numbers.

Adding these columns to each parent's object just does not make sense. There is no supporting case, at least in this system, where it would make sense to add all these extra nullable columns to each parent object's table. Abstracting it to the separate table is the most logical route.

The challenge again then is mapping these phone numbers to variying parent objects. The solution I am leaning towards is adding the parent id and parent type columns to each phone number so that querying id "123abc" for parent "Manager" returns X amount of phone numbers for that particular business object owner. Again, the issue is that these phone numbers could remain orphaned as there is no foreign key constraint on the parent ID column as that ID could be mapped to many different business object owners.

G.