Re: Question on Structuring Product Attributes

In article <1601143370402385874.040013hidders-gmail.com_at_news.xs4all.nl>,  Jan Hidders <hidders_at_gmail.com> wrote:

> Derek Asirvadem <derek.asirvadem_at_gmail.com> wrote:
> > This one should not pass unnoticed.
> >
> > On Monday, 18 February 2013 09:09:15 UTC+11, Eric wrote:
> >>
> >> To quote from Codd[1970]:
> >>
> >> "A firstorder predicate calculus suffices
> >> if the collection of relations is in normal form."
> >
> > Codd specifies what that Normal Form is, that reference is not merely a
> > generic or general term.
>
> Indeed. Also note that Codd's claim is not unproblematic. Even if you
> restrict yourself to the flat relational model, first order logic cannot
> express many practical queries. So what exactly does he mean by
> "sufficient" here?

I interpret that quote as follows: "If we allow relations as attribute values, we need (at least) a second-order relational calculus". In this sense, first-order logic "suffices" when relations are "flat" (we don't need to quantify over relations). Of course I agree with you, many interesting queries cannot be expressed in FOL, but you can always design a query language with additional power (SQL is an example).

Nicola Received on Wed Oct 02 2013 - 20:55:36 CEST