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Re: RM and abstract syntax trees

From: Bob Badour <bbadour_at_pei.sympatico.ca>
Date: Tue, 30 Oct 2007 15:22:26 -0300
Message-ID: <47277664$0$14879$9a566e8b@news.aliant.net>


paul c wrote:

> paul c wrote:
> ...
>

>> (ps: I don't agree that RM can't represent nested lists but I would 
>> agree that it's not much fun to manipulate them, I wish Codd had said 
>> more about nested relations as I have a feeling he spent some time 
>> considering them.)

>
>
> Here's my favourite nested relation, although I admit it's probably
> useless in practice. It's a recursive one. Sorry I don't have much
> mastery of conventional syntax, what I mean here is something like R:
> <attribute list> where <attribute list> is a set of attribute name,
> attribute type pairs and typeof is swiped from C-language:
>
> R: (A typeof R)
>
> I don't know how to display a value for R but I guess it could have
> either no tuples or one tuple.

It could have any number of tuples. See formalism under "philosophy of mathematics".

Example values are:
zero tuples:
{}

one tuple:

{{}}
{{{}}}
{{{{}}}}
{{{},{{}}}}

...

two tuples:

{{},{{}}}
{{{}},{{{}}}}
{{},{{{}}}}

...

three tuples:
{{},{{}},{{},{{}}}}
{{},{{}},{{{}}}}
...

four tuples:
{{},{{}},{{},{{}}},{{},{{}},{{},{{}}}}}
etc.

> Also guessing that R <OR> (<NOT> R) has one tuple and R <AND> (<NOT> R)
> has no tuples (where <OR>, <AND>, <NOT> come from D&D syntax).

I suspect you guess incorrectly for at least one of them. Received on Tue Oct 30 2007 - 13:22:26 CDT

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