Re: [xml-dev] XML vs relational database

[Sylvain LOISEAU <sylvain.loiseau@wanadoo.fr>]

>> Don't you think there is a structural
>> difference, from this point of view, between XML and DBMS?

> Sure, in SQL all the instances have the same structure, so the structure
> information can be stored separately from the instances.

Ok. But I'm not sure to have completly understand. With SQL, there is no need to store the structure information with the instance, but is this _possible_? For instance, one can ask for a structural property of the tree, in XPath, say the name of an element, by (1) referring to this element by its position and (2) using local-name() : local-name(./children[1]). In a relational algebra model, there is no order of the field, if I understand correctly. I see no other way of adressing a field than by its name.

I'm not sure I'm saying something trivial (a set doesn't have the properties of a tree) or not (there is a structural difference between sql and xml regarding the relation between data and metadata).

Sylvain

-- 
Sylvain Loiseau
sloiseau@limsi.fr
http://www.limsi.fr/~sloiseau
 
On peut pratiquer objectivement, c'est-à-dire impartialement,
une recherche dont l'objet ne peut être conçu et construit
sans rapport à une qualification positive et négative, dont
l'objet n'est donc pas tant un fait qu'une valeur.
 
Canguilhem, /Le normal et le pathologique/, p. 157