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From Henning von Bargen <H.vonBar...@triestram-partner.de>
Subject AW: [vote] A native XML database project under Apache
Date Fri, 19 Oct 2001 08:19:35 GMT
Believe me, I know RDBMSystems and I know what a tree is.
I've developed with DB2 and Oracle since 1990.
The problem with tree structures and relational databases is
that none of the existing systems can handle a set of sets effectively
in the general case, or to use the terminology of SQL,
a table can not contain another table.
A simple master-detail relationship like dept/emp or order/items
involves a master table (dept) and a child table (emp).
To notify the relation between these tables you have to include
the primary key of the master table in the detail table.
(this is like a pointer from a node to its parent node in the tree).

If your data is well structured like this dept/emp, it is
a very good choice to use a RDBMS,
because the definition of tables and columns is more or less fixed.

But if you have trees with a greate depth, like SVG documents etc.,
your natural approach would imply that you had to create
tables for every kind of node.
You end up with several thousand tables even for a very small
database, and you have to create/drop tables and indexes all the time.
Existing databases can not handle that effectively.

Henning

> -----Urspr√ľngliche Nachricht-----
> Von:	Robert Stuart [SMTP:Robert.Stuart@NFER-NELSON.co.uk]
> Gesendet am:	Freitag, 19. Oktober 2001 10:05
> An:	'general@xml.apache.org'
> Betreff:	RE: [vote] A native XML database project under Apache
> 
> Relational database theory derives from set theory.  (EF Codd circa 1980)
> 
> A tree structure may be viewed as a set of branches each containing a set
> branches and leaves.
> 	The root is simply a branch with no parent branch.
> 	A leaf is simply a branch with no child branch.
> 
> Thus, we are mapping one set-of-sets onto another set-of-sets.
> 
> 
> -----Original Message-----
> From: Henning von Bargen [mailto:H.vonBargen@triestram-partner.de]
> Sent: 19 October 2001 08:49
> To: 'general@xml.apache.org'
> Subject: AW: [vote] A native XML database project under Apache
> 
> 
> > -----Urspr√ľngliche Nachricht-----
> > Von:	Robert Stuart [SMTP:Robert.Stuart@NFER-NELSON.co.uk]
> > Gesendet am:	Freitag, 19. Oktober 2001 09:45
> > An:	'general@xml.apache.org'
> > Betreff:	RE: [vote] A native XML database project under Apache
> > 
> > Any XML document, by definition, must be represented by a tree
structure.
> > This means that, for all valid XML documents have a clearly defined
> > structure.
> > 
> > Tree structures map, very naturally, into relational databases (pun not
> > intended). 
> > For the rest of this note, any reference I make to a database (db),
assume
> I
> > mean a relational database.
> 
> Sorry, I can't follow you.
> Your are right that XML is a tree structure.
> But how can a tree structure map naturally into relational databases?
> 
> >
> > XML documents may (optional) have meta-data associated with them (DTD,
or
> ...
> > 
> > Robert Stuart
> > 
> 
> Henning
> 
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