Re: repeating groups

From: Jon Heggland <>
Date: Mon, 20 Feb 2006 18:02:57 +0100
Message-ID: <>

In article <>, says...
> There are many and varied proposals being thrown around (which is a
> *good* thing) and they have various degrees of associated complication.
> Some of this complication would be at the logical level, and some
> would be at the implementation level.
> If we do nothing else but add list attributes (one of the least
> complicated
> proposals) then we have to at least be able implement deep list
> equality checking, for example. (You have to be able to test equality
> for all attribute types to do an equijoin.)

I wouldn't say that affects the relational algebra as such, though. When I design and implement types in Dataphor, I hardly think of myself as changing or extending the RA.

> We also need to figure out what list operations we're going to support,
> and the field of "list algebra" seems much less clear to me than
> the field of set algebra.

This neither. It is exactly the same problem you face every time you add a new type to a relational database.

> If we add lists as top level entities, then we have to figure out
> how the top-level set operations interact with the top level
> list operations. What happens when we append a list to a set?
> What happens when we join a list to a set? A list to a list?
> This also affects closure, which makes it really important.

This *does* affect the RA, but this is something very different from having lists as *attributes*, which I though was what was being discussed.

But thank you. I was afraid I had missed something, but it was just a question of precision and terminology, as it often is. :)

Received on Mon Feb 20 2006 - 18:02:57 CET

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