Re: Example of expression bias?
Date: 20 Jun 2006 23:33:00 -0700
Message-ID: <1150871580.921882.100400_at_p79g2000cwp.googlegroups.com>
J M Davitt wrote:
> paul c wrote:
> > Tony D wrote:
> >
> >> ...
> >>
> >>> A data type in RM = (a domain1 to draw values from) + (restrictions
> >>> implemented on domain1 --> domain constraint) + (operators that can be
> >>> defined using that data type)
> >>> ...
> >>
> >> This may be one definition of a data type (not quite one I'd accept, as
> >> we've thrashed over elsewhere), but there is nothing particular to RM
> >> about this.
> >> ...
> >
> > "domain constraint" seems an uncommon term to me because we usually talk
> > of constraints on relations. but I often puzzle over constraints,
> > thinking that they could be as fundamental as any other notion, e.g.,
> > once one arrives at a similar conception of relations to Codd's, one
> > could view everything that one does with them as either adding or
> > subtracting constraints.
>
> CJD calls them type constraints; they define the set of values
> that constitute the type. Types are named, so the sets are named.
>
> The only thing I'd argue about in Cimode's definition is that
> operators are part of the data type. In fact, D+D make the point
> that the declaration of operators is orthogonal to the declaration
> of types -- given that the types are extant before the operators.
No need to argue on that, operators are indeed a part of a data type definition. I would personally define *possible* operators applyable at domain level then define attribute *permissible* operators at data type level . The point of the exchange with Tony D was to make him understand that a data type is a definition of rules that allows to establish the permissible values that can be extracted from a domain...
> > p
Received on Wed Jun 21 2006 - 08:33:00 CEST