Re: 1GB Tables as Classes, or Tables as Types, and all that refuted

From: Alfredo Novoa <alfredo_at_ncs.es>
Date: Wed, 24 Nov 2004 16:56:14 GMT
Message-ID: <41a4bcf4.21479484@news.wanadoo.es>

On Wed, 24 Nov 2004 16:26:18 +0100, "Ja Lar" <ingen_at_mail.her> wrote:

>> An attribute of a relation can not have another relation as its
>> domain. This is an absurd.
>
>I recommend you Date's Intro ...(8th ed), Part II/The Relational Model p.
>152: Relation-Valued Attributes.
>You might want to inform him about the absurdity :-)

No, you are missing the point. Relation valued attributes don't have a relation value as their type (domain), they have a relation type as their type.

For instance:

var CandidateKeys real relation { RelVar Char, Attributes relation { Attribute Char } } key { RelVar, Attributes };

Here "relation { Attribute Char }" is a relation type generator that generates a relation type for the "Attributes" attribute.

Regards Received on Wed Nov 24 2004 - 10:56:14 CST