> If the blob holds a single value (eg: "movie"), why is it wrong?

And you want to deprecate

SELECT * FROM myTable WHERE movieTypeUDF(myBlobColumn, 'AVI')

queries?

> There are plenty of systems with hundreds or thousands of
> tables. If this is what it takes to guarantee data consistency,
> fine with me.

No, but you do not define a table on per entity basis, i.e. for each
new entity new table. Do you?

> The problem I see with XML as a single entity and operators
> to query/massage its value, is that in the examples given, it
> doesn't make sense at all.
>
> It duplicates data, it puts a burden on consistency etc etc...
>
> Take the example from earlier on -- it had books and authors
> and you can store "Published" with it as well, right?
> Now what happens if the publisher changes name? You have
> to go through all (or let the XML-DBMS do it) to change all
> values (of type "XML") and look for a certain node...

Wrong. I do not update publisher there. Because at the time when book
was published the publisher had an old name. You just do not update
that document - document is perfectly consistent and its contents is
correct.

If a girl marries somebody and changes her surname, she does not start
to change her maiden-name on all her schoolbooks, does she?

> Sounds messy.

If you try to apply relational point of view to XML model - yes. That
only means you don't understand it correctly. Same as people that have
learned structured programming are doing their first stept in
object-oriented world. They simply think wrong.

> People might want to rethink if storing complete documents is the
> "way to go". It's not like we have come up with some silly
> requirement the last 2, 3 or 4 years that suddenly makes it
> impossible to store data into a relational based DBMS. What is
> happening here, is that people invent a new query language to work
> around problems: multi value stuff in a single "value" (namely: the
> XML document).

Wrong. People just want to work with the documents in a natural way
they are used to. They want to add semi-structured notes to the
documents and want to be able to query that documents. That does not
really fit the relational model, and you want them to restrict with it.

> > I meant relationships like grandfather-grandchild. You do not have
> > explicit relation using some surrogate key.
>
> Ah, but in an XML document, this relation is "described" with the
> "nodes". Do I get it now?

No, I did not mean nodes there. I was talking about the order. It is
just there.

> It couldn't store anything you like :-) That's what was wrong.

So can't the relational model too. Not anything, at least not in a
natural way.

Roman