Re: Proposal: 6NF

From: Jan Hidders <hidders_at_gmail.com>
Date: 7 Oct 2006 00:13:43 -0700
Message-ID: <1160205223.897554.138210@b28g2000cwb.googlegroups.com>

dawn schreef:

> What is an accurate generalization or abstraction from Pick? What are
> the precise features that permit this example of a function with null
> in the range of a function within the dbms environment? I thought the
> 2VL was a key factor in null being a value rather than a non-value as
> it is in SQL.

Close, but not exactly. In the context of database theory the most relavant definition of a value is:

Something that can be stored in a computer and for which an equivalance relation is defined over its representations that defines equality.

Since in SQL it does not hold that NULL = NULL the notion of equality is not an equivalence relation (which must be reflexive, symmetric and transitive) so by the above definition SQL does not treat NULL as a value.

Jan Hidders

Received on Sat Oct 07 2006 - 02:13:43 CDT