Re: what are keys and surrogates?

On Jan 8, 6:17 pm, David BL <davi..._at_iinet.net.au> wrote:
> On Jan 8, 9:26 am, JOG <j..._at_cs.nott.ac.uk> wrote:
>
> In November I started a thread called "RM and abstract syntax trees"
> in which I suggested that RM was poorly suited for the representation,
> never mind manipulation of ASTs.

Hmmm, I think I remember that. ;-)

> The problem is that the only
> reasonable way to represent the structure is to introduce meaningless
> node identifiers. An important principle in the RM is that a tuple
> should always represent a proposition that makes sense to the problem
> domain expert, so I agree with you that we cannot allow hidden
> identifiers. Therefore the RM cannot help but expose the node
> identifiers for all to see.
>
> Prolog is able to parse string expressions entered by users and build
> and manipulate ASTs. Behind the scenes, nested functor expressions
> are usually implemented using dynamically allocated nodes wired up
> with pointers. However, as far as the programmer is concerned, only
> unification is available to decompose the structure. It seems to me
> that Prolog has a more general support for data modeling than
> available in the RM, to the extent that nested functor expressions
> avoid the need to introduce lots of meaningless identifiers.

This issue goes away if we relax 1NF and allow attributes that are lists or relations. This gives us nested structures. (Nested relations are not particularly controversial around here.)

Marshall Received on Wed Jan 09 2008 - 05:25:23 CET