Re: RM and abstract syntax trees

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.
.

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