Re: RM and abstract syntax trees

paul c wrote:

David BL wrote:

On Oct 30, 6:29 pm, "Roy Hann" <specia...@xxxxxxxxxxxxxxxxxxxxx>
wrote:

"David BL" <davi...@xxxxxxxxxxxx> wrote in message

news:1193713604.283167.146850@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx

In the following I compare different techniques for representing an
Abstract Syntax Tree (AST), concluding that RM is poorly suited.

[snip]

I anticipate that this rule of thumb provides a useful insight on that
rather vague notion of "semi-structured data". ie it explains exactly
when and why there is data that is not suitable for direct
representation in RM.

Education triumphs over learning once again.

Roy

Please say what you disagree with. I can take it.

Okay, from your original post:

"So RM is forced
to expose the equivalent of pointers directly in the representation.
Furthermore, the RM has no mechanism for hiding these pointers or
giving the user an interface that promotes the idea that a node
logically represents a value."

Where does RM ever mention pointers? Eg., What are the pointer operations that RM supports?

(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.)

It seems he considered them unecessary in the sense one can always normalize the data to obviate the need for them.
.

Relevant Pages

  • Re: question on structs and memory blocks
    ... MyStruct and in fact it is better to do so since sizeofincludes any ... but merely pointers to them, it is the cost of these pointers that ... To reconcile their idiosyncratic internal representations, ... the two machines must agree on a common external representation ...
    (comp.lang.c)
  • Re: ptr conversions and values
    ... >> precision complex number can have the same representation as a double. ... >> There's no sense in which a memory location and an integer are the same ... The standard doesn't either. ... What do pointers to _different_ struct types have in common ...
    (comp.std.c)
  • Re: ptr conversions and values
    ... > A complex number is not an array, ... representation, without providing an explanation of what pairs of values are ... to say it about pointers and integers. ... >>> and joins it with a complex type that expresses the same value. ...
    (comp.std.c)
  • Re: ptr conversions and values
    ... That's why the standard explicitly ... > representation, without providing an explanation of what pairs of values are ... So I have given an explanation how to connect integers to pointers ... > won't have any more or any less issues than conversion does. ...
    (comp.std.c)
  • Re: Functions taking pointers to different types as arguments
    ... Pointers to functions are *interconvertible*. ... Consider int and double: we can take an int value, ... but the conversion has changed things internally. ... use the same representation for int and double. ...
    (comp.lang.c)