On Friday 2006-06-09 09:50, Martijn van Oosterhout wrote:
> On Fri, Jun 09, 2006 at 12:01:07PM -0400, A.M. wrote:
> > So you should normalize and add relations to represent the state
> > adequately. NULL doesn't give you enough information anyway- does NULL in
> > a birthday header mean "no birthday", "n/a" (a business doesn't have a
> > birthday), "not born yet", etc... Using real data, you can represent any
> > of these states.
>
> What's makes you think I'm interested in storing the distinctions?
> Either I know the birthday or I don't. If I want to work out why I
> don't know it, yeah, it's worth storing the state. There are other ways
> of finding that out (for example you can readily tell if you're looking
> at a business and I know the system doesn't have people that aren't
> born yet). But mostly I just need to track that it's not known.
>
> Have a nice day,
More importantly, it is usually not possible to list all the reasons
information might be absent. Nullity is a semantically empty residual
category. It can and does mean all unspecified (or accidental) forms of
information absence. You need null when you model data because real data is
not always amenable to an exhaustive partition.