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Home -> Community -> Usenet -> comp.databases.theory -> Re: Relational lattice completeness
vc wrote:
> Jan Hidders wrote:
> > vc wrote:
> > > Jan Hidders wrote:
> > > > vc wrote:
> > > > >
> > > > > What's confusing, to me at least, is that in another thread you said
> > > > > that the question was about complete theories, that is about
> > > > > completeness in the context of the first incompleteness theorem.
> > > >
> > > > It is. Because we talking about a system where we have a semantical
> > > > notion of truth for algebraic identities and a syntactical one
> > > > (derivation from the set of given algebraic identies by applying them
> > > > to each other) and the question is if these two are the same.
> > >
> > > They would be the same for a complete (in the sense of the first
> > > incompletenes theorem) system so finding out whether this is the case
> > > would amount to showing if the system in question is complete or not.
> >
> > Not necessarily because the syntactical notion of truth is not the
> > usual one. It's related but not the same.
>
It also doesn't mention completeness, so I thought you meant the notion of completeness that it is usually assumed to say something about. But this is all detracting form the main point. I gave an exact and, I think, very simple definition in:
http://groups.google.be/group/comp.databases.theory/msg/a1c140fbe76681e8?hl=en&
What did you not understand about it?
> Let's assume that by 'syntactical notion of truth; you've meant in fact
> derivation. If so, what did you mean by " because the syntactical
> notion of truth is not the usual one. It's related but not the same" ?
We have different derivation rules.
> > Having a full and simple axiomatization makes it possible to write
> > query optimizers that do a more thorough search of the "optimization
> > space", and if you know you are complete then you are sure that you
> > need not look further for any other rules.
>
But you are not sure that you can find all possible query evaluation plans, so you migh miss an optimization opportunity.