Re: Objects and Relations

From: Cimode <cimode_at_hotmail.com>
Date: 26 Feb 2007 04:18:49 -0800
Message-ID: <1172492329.307972.288950_at_s48g2000cws.googlegroups.com>


On Feb 26, 11:20 am, "Alfredo Novoa" <alfred..._at_gmail.com> wrote:
> On 24 feb, 13:43, "Cimode" <cim..._at_hotmail.com> wrote:
>
> > If you define class by domain then what is the RM equivalent for
> > relation?
>
> You probably mean the OO equivalent for relation.
>
> OO lacks an equivalent for relation. That's why it is so difficult to
> write database applications using OO languages.
Noted.

> > In RM, a domain is *not* the same* as a type or a relation.
>
> In RM domain is used as a synonym of type and it is completely
> different to relation.
Disagreed. You can not equate both.
> > (
> > domain = set of *possible* values for which a relation draws
> > *possibly* values
>
> When you say "relation" we assume that you mean "relation value". If
> you mean "relation variable" please write: "relation variable" or
> "relvar".
Thank you for your educational intent I already know that.

No, relations are equated to relation values only in the computing community. I prefer to keep the mathematical distinction between relation and relation value.

> On the other hand, a domain is a set of any kind of values: scalar,
> relational, tuple, array, etc.
>
> > typing = making a domain from a relation body and name (therefore
> > only *existing* values for a specific relation).
>
> I don't see any sense here.
Meaning that a domain potentially defines a type. It becomes a domain only when values are drawn from it. It is a subtlety that is necessary to truly understand RM.

> Regards
Received on Mon Feb 26 2007 - 13:18:49 CET

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