Re: Base Normal Form

In article <AuGye.16814$pa3.328_at_newsread2.news.atl.earthlink.net>, david.cressey_at_earthlink.net says...
> What's the difference between calling a table a list of tuples, and calling
> a table an array of tuples?

In some formal contexts, I think a list is either empty, or consisting of an element and a tail, which is also a list. In contrast, an array is a sequence of elements that can be referred to by ordinal position. In this case, there is no significant difference, I think.

> I'm hazy on the distinction between a relation and a relvar.

"Relvar" is short for "relation variable". A relvar can hold a relation value, just like an integer variable can hold an integer. "Relvar" corresponds to TABLE in SQL; a relation value is the value (contents) of a table at some time. Updating a table is really assigning a new relation value to the relvar (though in many cases, the new value closely resembles the old).

Most literature use "relation" for both "relation variable" and "relation value", and depend on context to make the meaning clear. Alternatively, they dismiss the notion that there is a difference.

-- 
Jon