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On Wed, 27 Aug 2003, Jeff Lowery wrote:
> > (b) XML also allows us various ways of representing relationships: like
> > parent-child, IDREF, or foreign keys. Each representation might be
> > "convenient" for the user for different applications..
> This is the key advantage of using XML to view data: many relationships can
> naturally be described hierarchically. Or, at least, we as humans see such
> hierarchies as natural.
> Relational purists will say tables and rows can represent such hierarchies,
> and do so in more flexible manner with better integrity. Fab Pascal, in his
> "Practical Issues in Database Management" book, chapter 7, gives an example.
> The problem is that he needs a diagram to illustrate the heirarchial
> relationships between table rows, because the hierarchy is far from obvious
> when looking at the table rows alone. He could have just as well, instead
> of a diagram, used XML elements; it would have been just a clear. ;-D
the thing is w.r.to expressiveness, all models are equivalent (I think)..
Only thing is ease of use, is it natural etc.. That depends on
application, I think we cannot generalize, we should wait and see what
people do when we provide products for relational/XML models...
Fabian Pascal is a good friend of mine too. His main point is sometimes we
do not ask right questions, which I think is very correct often times
w.r.to myself at least.. He did mention that if I had listened to him
before I started my work, he would have convinced me to work on issues
such as: recursive operators for relational model, rather than working on
XML directly.. "convenient" recursive operators such as // are also
advantages that XML provides.. again that is largely possible because XML
provides recursive types.. relational model right now provides recursive
operator using infix operator, which is not very easy to write..
I do have a copy of Fabian's book, I will take a look at the example you
The broader question is: Is XML useful as a logical model, I do not think
we need to discuss XML as physical model...
cheers and regards - murali.