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Re: XML vs relational database

• From: Rick Marshall <rjm@z...>
• To: Len Bullard <cbullard@h...>
• Date: Fri, 17 Aug 2007 11:57:32 +1000

I haven't followed this too closely and so I'm probably going to 
reinvigorate another perma thread or something - but here goes.

There are several types of XML files (generic - not the specification 
kind) and of most interest to database people is the one where nodes 
consist of tags or data but not both. The inverse I suspect is true for 
document people.

The former can be translated easily into a relational scheme (even if it 
is recursive and/or requires normalisation) while the latter can't.

The other fundamental problem is that XML implies ordering amongst nodes 
and content - relational schemes don't. Relational schemes in fact don't 
even tell you how the columns are organised - just that they exist 
(although this might not be obvious at first from the standard texts).

On the other hand relational data can be easily inverted (ie look from 
the bottom up rather than top down) and the relationship between nodes 
can be easily redefined. XML requires external indexing or rewriting to 
do this.

Which brings me to the most fundamental difference - XML is the data, 
relational schemes are ways to access and modify the data.

Rick

Len Bullard wrote:
> From: Jim Melton [mailto:jim.melton@a...] 
> Sent: Thursday, August 16, 2007 5:40 P
>
>   
>> Len, as you know, I work for a company founded on and based on SQL, 
>> and I may be prejudiced.  
>>     
>
> Of course.  I'm a fan of cheap standard tuners for the same reason.  Tools
> and pay for tools.  
>
>   
>> But that doesn't mean that I'm blind.  
>>     
>
> Not meant or implied.  History is what it is because we make our best
> choices at a time and the conditions of the time set the where clauses, if I
> may be pseudoC-Phil.
>
>   
>> I am a great proponent of helping integrate all sorts of technologies into 
>> the SQL environment -- as long as it is meaningful and useful to 
>> those annoyances that pay my salary...customers.  That's why I 
>> participated so actively in the development of ORDBMS (adding object 
>> capabilities to SQL) in the 1992 - 1999 timeframe, and why I have 
>> been so passionate about adding the XML type and XQuery integration 
>> into SQL starting in about 2001 or 2002.
>>     
>
> Indeed.
>
>   
>> But you won't find me claiming that SQL does everything.  
>>     
>
> The books I read basically say if one needs to do fast complex logic or
> parse strings, stick with the C#/Java classes.  If one needs to manipulate
> data fast and reliably, stick with SQL.  XML is a case of a syntax being
> used as a fuzzy blueprint for a storage representation but essentially, it
> is serialization by application objects, or from another view, a pretty-good
> if optimized in-memory application db.
>
> Then is comes down to screen flash.  Frame rate: the final frontier. :-)
>
>   
>> It's significantly worse at handling arbitrary tree structures, which is
>> why we integrated XQuery into SQL/XML instead of trying to train SQL itself
>> to do the job.
>>     
>
> The need is to understand when to use which for what.   XML has an advantage
> of being a document given humans are very good at fast loose tree
> construction.  They manage nesting as a concept pretty well.   Good set
> design is a different talent and requires some stiffer discipline and
> understanding.  The payoffs of combining these is that in systems building
> where we integrate information from people with different skill sets, we can
> keep both busy.  Thus, Money.  And that's a good thing or so our spouses
> tell us.
>
>   
>> Hope this helps,
>>     
>
> Always!
>
> len
>
> At 8/16/2007 03:47 PM, Ken North wrote:
>   
>>>> We wouldn't have anything.  The outcry would have been "SQL does 
>>>>         
>> all of that
>>     
>>>> already".  If the counter arguments had been one metalevel above 
>>>>         
>> the current
>>     
>>>> understanding of the hordes of commenting parties, the political battle
>>>> would have been over right there.
>>>>         
>> Let's distinguish between the storage engine used for an SQL product and
>>     
> the
>   
>> query language itself. Even though the storage engine of an SQL product
>>     
> might
>   
>> handle nested sets, the SQL query language of that era wasn't powerful
>>     
> enough
>   
>> for a reasonable person to argue "SQL does all of that already".
>>     
> Capabilities
>   
>> such as XML schema mapping or using a DTD or schema to validate query
>>     
> results
>   
>> were beyond the scope of the SQL language of that time.
>>
>> It would surprise me if Jim Melton feels updating the standard from SQL-92
>>     
> to
>   
>> SQL/XML has been a slam dunk.
>>     
>
> ========================================================================
> Jim Melton --- Editor of ISO/IEC 9075-* (SQL)     Phone: +1.801.942.0144
>    Co-Chair, W3C XML Query WG; F&O (etc.) editor    Fax : +1.801.942.3345
> Oracle Corporation        Oracle Email: jim dot melton at oracle dot com
> 1930 Viscounti Drive      Standards email: jim dot melton at acm dot org
> Sandy, UT 84093-1063 USA          Personal email: jim at melton dot name
> ========================================================================
> =  Facts are facts.   But any opinions expressed are the opinions      =
> =  only of myself and may or may not reflect the opinions of anybody   =
> =  else with whom I may or may not have discussed the issues at hand.  =
> ======================================================================== 
>
>
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• References:
  • RE: XML vs relational database
    • From: "Len Bullard" <cbullard@h...>