Re: Lucid statement of the MV vs RM position?

Marshall Spight wrote:
> Jon Heggland wrote:

>> No, I think that's right. In the resulting relation, the set of
>> attributes that were not grouped, functionally determines the RVA. That
>> follows from the definition of GROUP.

I think not; not the TTM GROUP that I'm discussing, at least. It's a relational operator: relation in, relation out. It is equivalent to / shorthand for a projection and an extension, I think.

That said, I guess GROUP could also be defined as a SUMMARIZE with an aggregate operator (or "summary"; TTM distinguishes between them) that computes the RVA value based on a set of attributes. That aggop/summary would be a bit non-standard, though, since it would need take a variable number of arguments, not just one. That still wouldn't make GROUP an aggregate operator, though.

> And wouldn't the above be true
> for any aggregate operator? Replace GROUP with SUM, for example.

Summaries are functionally dependent on the attributes they are grouped by, yes. I do see the similarity you point out.

> (I don't know if D&D consider GROUP an aggregate or not, but
> it certainly meets the definition AFAICT.)

What definition is that? That's perhaps the most important point. :)

-- 
Jon