Re: completeness of the relational lattice
Date: Fri, 22 Jun 2007 13:14:57 -0700
On Jun 22, 12:59 pm, Marshall <marshall.spi..._at_gmail.com> wrote:
> On Jun 22, 12:42 pm, Jan Hidders <hidd..._at_gmail.com> wrote:
> > On 22 jun, 20:36, Marshall <marshall.spi..._at_gmail.com> wrote:
> [lots of agreement snipped]
> > > In simplified terms, you're proposing that we allow the
> > > construction of relations with a specific set of attributes
> > > and a specific body (namely: empty.) I'm proposing that
> > > we only allow the construction of relations with a specific
> > > set of attributes. Hence my proposal introduces fewer
> > > concepts, therefore it is simpler, and we should by default
> > > choose the simplest alternative that gets us what we
> > > need.
> > Let me see if I understand. So you propose a constructm, say [X] with
> > X a set of attributes, with the semantics that it returns an arbitrary
> > relation with header S.
> Ack, no!
May I suggest that there is no concept of relation construction other than specifying it in terms of other relations via primary lattice operations? So given any relation we can easily construct an empty relation with the same set of attributes. On the other hand, given an empty realtion, there is no way to construct nonempty relation, unless there are some other relations that we can leverage to.
Also in relational model when we speak and think in terms the set of the attributes. Sometimes we even have to bring up the concept of tuple -- a concept that standard RA completely eliminated. What I'm suggesting is that removing the concept of attributes would benefit us the same way as abstracting away the concept of tuple. Therefore, I repeat, the thesis:
"set of attributes" = "empty relation" Received on Fri Jun 22 2007 - 22:14:57 CEST