Re: database design method

Lauri Pietarinen wrote:
>Jan Hidders wrote:
>> Another thing I wondered about while reading it is if I can express the
>> NEST and the UNNEST operations of the nested relational algebra. I seem to
>> remember that Date & Darwen were heavily opposed to those operations, but
>> the language would otherwise be certainly computationally incomplete. So,
>> can I?
>
>I took a look at the printed version of TTM (2ed)
>(which is not available on line).

This is of course their good right but I hope the authors realize how much better for the acceptance of their model it would be if it were on line. Think of ODMG/OQL and W3C/XML.

>On pages 137-138 there is a discussion of NEST and UNNEST
>(in Tutorial-D the operations are called GROUP and UNGROUP).

Wow!! Do you realize what this means? Chris Date has recanted! The relational model is dead, long live the nested relational model. We can finally kiss the 1NF good bye. Good riddance, I say. I think I'm beginning to like Tutorial-D. :-)

So can I abuse you a little more as my tutorial-D tutor? :-) Can I have recursive types? For example (probably not the right syntax, but I think you will understand what I mean):

TYPE Tree = TUPLE { NODE-VALUE STRING, SUBTREES RELATION { TREE Tree } }

• Jan Hidders