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RE: Question for updating existing XML file

• To: "Michael Kay" <michael.h.kay@n...>,"Jim Rankin" <jimbokun_lists@m...>
• Subject: RE: Question for updating existing XML file
• From: "Hunsberger, Peter" <Peter.Hunsberger@S...>
• Date: Wed, 28 Jul 2004 10:19:26 -0500
• Cc: "'xml-dev' List" <xml-dev@l...>
• Thread-index: AcRz6i5Tq3R05BsNQ3qWei5YYHb2FgAmdNAQAAxJEFA=
• Thread-topic: Question for updating existing XML file

Michael Kay <michael.h.kay@n...> writes:

>> At one time hierarchical and relational databases were competing
technologies, 
>> but overall the relational model, and relational databases, won out.
The 
>> relational model is now more developed and generally accepted to be
superior 
>> to the hierarchical model for most uses. (Please correct me if I'm
wrong or 
>> oversimplifying here.) 

> You are over-simplifying, because there has never been a single
hierarchical 
> model for databases. Most of the database textbooks equate "the
hierarchical 
> model" to the IBM IMS product, and most of the weaknesses of that
generation 
> of technology are nothing to do with its data model. The biggest shift
from 
> the hierarchic and network-model databases to the relational model was
the 
> move from procedural DMLs to declarative query languages, and of
course XPath 
> and XQuery (and OQL before them) prove that it's perfectly feasible to
use a 
> declarative query language over hierarchies and networks. In fact, the
power 
> of these languages is greater than that of the relational calculus
because it 
> extends to recursive queries.
>
> Probably the greatest weakness of XML as a data model for databases is
that it 
> doesn't provide a coherent way of modelling the non-hierarchical
relationships. 
> But that's a weakness of the relational model too.

I'm having a hard time parsing this.  Did you perhaps mean the inverse;
that the relational model has a hard time modeling hierarchical
relationships?  Or is this a general comment about the difficulties in
modeling for the relational model?  If it's the latter I'd disagree;
just about anyone can at least do a first normal form model.  That may
not get you real far, but tools abound as do training, books and tons of
best practices to fall back on.

A more general comment/question: it recently occurred to me that it is
likely possible to model any XML Schema as a relational schema (proof of
this theorem is left as an exercise for the reader  ;-)? Don't know what
that gets you, but as I've said at least the tools abound... 

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