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RE: merge mode for XML

From: Greg A. Woods
Subject: RE: merge mode for XML
Date: Fri, 3 May 2002 15:26:12 -0400 (EDT)

[ On Wednesday, May 1, 2002 at 13:33:08 (-0700), Glew, Andy wrote: ]
> Subject: RE: merge mode for XML
> Well, I wrote Perl-SQL, a relational database system that
> is self-schematizing - where every record can define its own schema,
> with its own fields.

Yeah, that sounds like something a perl hacker would do....

> Motivation: schema changes in most existing relational databases are
> onerous.

For very good reason.

> 3-4 years ago I discussed self-schematization with Prof. David Dewitt, a man 
> of some
> reknown in database circles.  His take is that self-schematization was not 
> done in the early days to save space, and that now it is not unreasonable to 
> do so.
> However, rather than Perl-SQL, he pointed to me towards XML, saying something
> like "well formed SQL doesn't require a schema or DTD -- that is the future."
> ---
> I.e., Greg, not all RDBMS experts agree with you about schemas; ditto DTDs.

I suspect Dewitt is thinking a little bit deeper than you suspect.
Certainly data can be self-describing -- that's what OO is all about.
OO databases can effectively be queried about their schemas, and since
all proper objects know how to interact with other objects, even those
in different classes (i.e. of different types), their relationships are

An RDBMS, however, is not an OODBMS.

Whether an XML document without a DTD and/or schema can be considered
self-describing enough to be independent like an object instance or a
set of object instances, is probably what you're trying to argue, but I
won't go any further since such a thing is strictly outside the scope of
XML proper and is way outside the scope of what a common tool like CVS
should ever deem worthy of dealing with.

                                                                Greg A. Woods

+1 416 218-0098;  <address@hidden>;  <address@hidden>;  <address@hidden>
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