Re: repeating groups

From: Marshall Spight <marshall.spight_at_gmail.com>
Date: 20 Feb 2006 08:34:02 -0800
Message-ID: <1140453242.747755.12070@g47g2000cwa.googlegroups.com>

Jon Heggland wrote:

> Can anybody please take half a minute to explain to a poor ignoramus why
> list attributes affects the (relational, I assume(?)) algebra? It seems
> to be taken for granted around here, but I can't figure out how/why.
> What am I missing?

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.)

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.

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.

HTH Marshall Received on Mon Feb 20 2006 - 10:34:02 CST