Proposal: 6NF - comp.databases.theory

Message from discussion Proposal: 6NF

Jan Hidders

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More options Oct 7 2006, 9:13 am

Newsgroups: comp.databases.theory

From: "Jan Hidders" <hidd...@gmail.com>

Date: 7 Oct 2006 00:13:43 -0700

Local: Sat, Oct 7 2006 9:13 am

Subject: Re: Proposal: 6NF

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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

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