RE: [xml-dev] SQL instead of XQuery

["Michael Kay" <mike@saxonica.com>]

> I'm agreed about effect on existing application - but i'm 
> implying all time, that we are making comparison of XML and 
> relational situation (instead of discussing of only one of 
> them). If we move to XML databases, effect on existing 
> application remains (non-triviality is not disappear !).
> 
> MK> XML is far more flexible in this regard.
> 
> Describe this flexibility, please, in light of said by me above.

Well, if an <employee> has <nationality> as a child, then it can always have
two <nationality> children by a minor change to the schema. This has far
less impact on applications than creating a separate table.
> 
> MK> It's also much easier to hold properties-of-properties
> 
For example

<employee>
  <nationality date-acquired="2001-05-06" checked="no">British</nationality>

Adding attributes like this will very rarely affect existing applications.

Also, the schema for an XML representation can be as strict or as liberal as
you choose, and instances can vary from each other as much as you like. In
SQL, if you add a column then you add it to every instance: it might be
null, but it is still there.

Michael Kay
http://www.saxonica.com/