Re: Expressing SQL in relational algebra
From: Neo <neo55592_at_hotmail.com>
Date: 9 Apr 2003 22:11:58 -0700
Message-ID: <4b45d3ad.0304092111.4a0d4a5b_at_posting.google.com>
Date: 9 Apr 2003 22:11:58 -0700
Message-ID: <4b45d3ad.0304092111.4a0d4a5b_at_posting.google.com>
> > Could the above also be expressed as "person ^ age ^ 20 ^ years ^
> > weight ^ 180 ^ pounds" where ^ means AND?
>
> Not that I know of. Where does the above indicate the restrict operation
> or the equality comparisons?
The intersection (^) operation fundamentally performs restriction because the resulting elements must be members of both sets (operands). Yes, each thing in the expression "((person)^((age)^(20)^(years))^((weight)^(180)^(pounds)))" is a set, class, or domain, in addition to being an element, instance or value at the same time. Received on Thu Apr 10 2003 - 07:11:58 CEST