Re: Database-valued attributes?

From: Marshall Spight <mspight_at_dnai.com>
Date: Tue, 11 Nov 2003 16:03:16 GMT
Message-ID: <8L7sb.170850$HS4.1382292@attbi_s01>

"Costin Cozianu" <c_cozianu_at_hotmail.com> wrote in message news:boqt6f$1g3h55$1_at_ID-152540.news.uni-berlin.de...
>
> I wouldn't call that an attribute. Because if you have a database call
> attribute a database is a collection of relations. Now you are no more
> in first order logic.

I want to make sure I understand you: you are saying that if I have a relation that contains tuples that are pointers to outside databases (or relations as well, presumably) then I have left the realm of first order logic. Yes? But that if I have a relation with an attribute type relation, or tuple of (relation, relation) then I'm still "safely" first order.

> However to your question, the answer is simple, once you have the
> following type constructors:
>
> TUPLE
> RELATION
> ARRAY
> LIST
What's the difference between array and list?

> So yes, you could represent that "tree" as a tuple with two elements,
> the base set and the adjacency list but then you've just accomplished
> very little.

Fair enough.

> Better try this one:
>
> type 'a tree = Empty | Node of 'a * 'a tree list

Mwa ha ha ha! But if I were asking about *that*, it would be on comp.lang.functional. And I probably won't be doing that until I finish reading "Haskell: the Craft of Functional Programming."

Marshall Received on Tue Nov 11 2003 - 10:03:16 CST