Re: Notions of Type
From: paul c <toledobythesea_at_oohay.ac>
Date: Thu, 17 Aug 2006 15:22:59 GMT
Message-ID: <nR%Eg.422634$IK3.267103_at_pd7tw1no>
>
> Yes.
>
>
>
> Very true. Of the various relational operators that have been
> identified over the years, only a few, like union, are really
> algebraic. RESTRICT, PROJECT, etc. aren't. ...
Date: Thu, 17 Aug 2006 15:22:59 GMT
Message-ID: <nR%Eg.422634$IK3.267103_at_pd7tw1no>
Marshall wrote:
> erk wrote:
>> Sorry if this is obvious to everyone else, but does an algebra include >> only operations defined on values of the type in question?
>
> Yes.
>
>
>> I ask
>> because in relational algebra, at least the rename operator involves a
>> different type ("attribute name") than the "core type" (relation).
>
> Very true. Of the various relational operators that have been
> identified over the years, only a few, like union, are really
> algebraic. RESTRICT, PROJECT, etc. aren't. ...
Just a quick question - is your reason for making that statement that restrict, project, etc. result in a relation that doesn't necessarily have all the attributes of the operand relations?
p Received on Thu Aug 17 2006 - 17:22:59 CEST