Re: Foreign superkey support

From: Marshall <marshall.spight_at_gmail.com>
Date: 8 Aug 2006 10:57:18 -0700
Message-ID: <1155059837.979156.61820@n13g2000cwa.googlegroups.com>

paul c wrote:

> Perhaps all I'm saying is that the basic relational algebra doesn't need
> a foreign key concept which I admit is a deviation from the specific
> question.

I don't think of constraints as being part of the algebra per se. Constraints
are a useful mechanism for ensuring integrity of variables, whereas the algebra is a way of constructing values from other values. (Including the values in variables.) Note that the algebra is what you do queries with, but constraints are relevant only when doing DML: insert, update, delete. (Although we may use the algebra to construct values that we then insert, for example.)

It is quite interesting to consider the idea of constraints as descriptive entities for values, in addition to being prescriptive for variables. We can then consider propogation of these descriptions through the algebraic operations.

> But as long as people like the shortcut notation, I think the
> example is a good reason for allowing super foreignkeys or foreign
> superkeys!

Frankly I think there's too much emphasis on foreign keys. I think we should emphasize the use of domestic keys wherever possible, and use foreign keys only when the domestic variety is not available.

Marshall

PS. dumb joke, sorry. Received on Tue Aug 08 2006 - 12:57:18 CDT