Re: Relational Lattice, what is it good for?
Date: 17 Feb 2006 15:17:05 -0800
Message-ID: <1140218225.392428.140550_at_o13g2000cwo.googlegroups.com>
Marshall Spight wrote:
[...]
> Conventions
>
> Relations are named with capital letters: A, B, C
>
> Sets of attributes are given with lower case letters, according
> to which relations these attributes appear in. Thus, (ab) is the
> set of attributes that are common to A and B. This set may be empty.
> The letters of the name are normalized to be in alphabetical order.
>
> The two operators of the Tropashko Algebra are written "&&" (natural
> join)
> and "||" (inner union.)
>
> We use set builder notation.
>
>
> Definitions
>
> A relation's attributes are unordered; we consider a relation (a,ab) to
> be the same type as a relation (ab,a) without further comment.
>
>
> Given
> A:(a, ab)
> B:(b, ab)
>
> The Natural Join, A && B is:
>
> { (a, b, ab) | (a, ab) in A and (b, ab) in B }
That does not make any obvious sense. What is '(a, b, ab)' ? Is it the union of sets of attributes [of their respective relations] or something else ? You did not define the expression. Received on Sat Feb 18 2006 - 00:17:05 CET