Re: circular relationships ok?

On 2 Mar 2006 18:51:01 -0800, "Marshall Spight" <marshall.spight_at_gmail.com> wrote:

>Gene Wirchenko wrote:
>> On 2 Mar 2006 15:35:41 -0800, "Marshall Spight" wrote:
>> >
>> >Okay. Let me adjust my phrasing:
>> >
>> >If that is the business rule, then are not Invoices and Orders
>> >the same SQL table?
>>
>> They might be, but need not be. 1-1 relationships are possible.
>> Again, consider husband and wife.
>
>I'm not getting it. If we're talking about husband and wife in
>a context in which there is exactly one-for-one always,
>then we are talking about a table of married people. In

     No. The husband and wife exist as separate entities and may be referred to individually. There may *also* be a table reflecting the marriages.

>which case, why wouldn't I have HusbandBirthday, WifeBirthday,
>etc.? In fact, I don't really see how the particular domain

     Because you probably want the birthdate of the person regardless of the role the person has in a marriage. People who are not married have birthdates, too.

>is even relevant; one can use cardinality relationships
>alone to make these decisions. If we didn't, we could
>just as well split every table of n attributes into n
>tables; the attributes are one-for-one after all.

[snip]

Sincerely,

Gene Wirchenko Received on Fri Mar 03 2006 - 14:14:39 CST