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From Kimbro Staken <ksta...@dbxmlgroup.com>
Subject Re: [vote] A native XML database project under Apache
Date Fri, 19 Oct 2001 08:02:11 GMT

On Friday, October 19, 2001, at 12:45 AM, Robert Stuart wrote:

> 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).
>

What type of mapping are you talking about? The type that would map a 
purchase-order element to a purchase order table or what I would call a 
native mapping where the purchase order element is mapped to an elements 
table? Either way it may be possible to get the data into the database but 
the cost will be high and retrieval can be very difficult. It will work 
fine for very small documents but beyond that the runtime cost will be 
extremely heavy and once you get into documents with semi-structured data 
and mixed content the non-native mapping style doesn't work at all.

I don't think I've ever heard anyone actually claim that tree structures 
map naturally to a relational database. Yes it''s possible to do it, but 
pulling the tree back together can be very slow and painful even when you 
have constructs like the connect by clause in Oracle.

BTW, some native XML databases are implemented using a native mapping to a 
relational database but most are not because it is highly inefficient for 
this particular problem.

> For the rest of this note, any reference I make to a database (db), 
> assume I
> mean a relational database.
>
> XML documents may (optional) have meta-data associated with them (DTD, or
> XSD).  This meta-data would simplify the design of a db, giving the
> relationship between tables - allowing us to populate the db structure as 
> a
> document is received.  (Note: this is a bi-directional operation, the
> meta-data in the db may be used to generate a DTD/XSD).
>
> The meta-data would not be essential in db design.
>
>
>
> I think I'd like to come on board with this one, how do I become a
> committer?
>
>
> Cheers
>
> Robert Stuart
>
>
> -----Original Message-----
> From: Eric van der Vlist [mailto:vdv@dyomedea.com]
> Sent: 19 October 2001 08:17
> To: general@xml.apache.org
> Subject: Re: [vote] A native XML database project under Apache
>
>
> Hi Stefano,
>
> Stefano Mazzocchi wrote:
>
>> Hi,
>>
>> while the world of native XML databases is full of marketing hype and
>> promises, it is evident (for all those who tried) that mapping general
>> XML schemas to relational databases can be sometimes very painful and
>> not very efficient.
>>
>> In fact, it is widely recognized from the database research community
>> that while well structured can be easily and efficiently mapped to a
>> relational database, less structured (often called semi-structured) data
>> is much more difficult to map.
>>
>
>
> Just for fun and also to take a step backward and evaluate the changes
> and invariants in our perception of XML systems, I couldn't resist
> reading some old emails exchanged two years ago!
>
> http://groups.yahoo.com/group/xml-server/message/32
>
> Enjoy :)
>
> Eric
> --
> Rendez-vous à Paris pour le Forum XML.
>                     http://www.technoforum.fr/Pages/forumXML01/index.html
> ------------------------------------------------------------------------
> Eric van der Vlist       http://xmlfr.org            http://dyomedea.com
> http://xsltunit.org      http://4xt.org           http://examplotron.org
> ------------------------------------------------------------------------
>
>
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>
>
Kimbro Staken
The dbXML Project
http://www.dbxml.org


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