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   Re: [xml-dev] XML and the Relational Model (was Re: [xml-dev] A standard

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At 02:30 PM 8/25/2003, pop3 wrote:
>I agree that mappings among models are useful.
>But I wish to note that the farther one gets away from the hardware the 
>less robust, slower and harder to optimize the resulting system becomes. 
>Specifically, if the application design for a terabyte system works out to 
>be a mapping between an rdbms and an XML tool like TeraText, and then a 
>separate, different mapping between the XML tool set back to a rdbms, then 
>my point is that the resulting system will have more failure points, be 
>harder to tune, and generally less robust than a "native" system.

You seem to like broad generalizations. Adding layers can improve 
performance - for instance, adding a cache or indexed access involves 
adding another layer of software, and either one does make the system more 
complex, but it also improves performance. Similarly, adding a query 
optimizer makes the system significantly more complex, but it does not 
really make it harder to use or hurt performance.

>Mappings, if you ask me, are bridges... like bridges they are an 
>infrastructure that is high maintenance and which require above normal 
>attention to support, and are subject to replacement periodically at high 

For our SQL/XML product, we have found that using the SQL/XML extensions 
generally results in faster programs than building the XML "by hand" using 
the DOM. The reason for this has a lot to do with the structure of the 
mappings between XML and relational, and the number of database calls 
required by the approaches people generally use when solving this problem. 
Here's a paper that discusses this at a useful level of depth:

         SQL/XML in JDBC Applications

I think this also applies to XQuery. It's pretty easy to imagine what it 
would look like to add a section on XQuery to the above paper.



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