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   Re: [xml-dev] XSLT 2.0 / XPath 2.0 - Assumptions

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5/12/2002 11:14:20 AM, Elliotte Rusty Harold <elharo@metalab.unc.edu> 

>At 11:03 AM -0400 5/12/02, Mike Champion wrote:
>>their careers and affiliations, it looks to me like the stated goal
>>is the real orientation -- a unification of RDBMS, OO, and XML 
>>approaches. As best I recall, the criticism from RDBMS folks has been
>>that it's too XML-centric.
>Where exactly does it state that? 


"One of the great strengths of XML is its flexibility in representing 
many different kinds of information from diverse sources. To exploit 
this flexibility, an XML query language must provide features for 
retrieving and interpreting information from these diverse sources."

"It is designed to be a small, easily implementable language in which 
queries are concise and easily understood. It is also flexible enough 
to query a broad spectrum of XML information sources, including both 
databases and documents. ... XQuery is derived from an XML query 
language called Quilt [Quilt], which in turn borrowed features from 
several other languages, including XPath 1.0 [XPath 1.0], XQL [XQL], 

Maybe "unification of approaches" is too strong, but clearly the 
objective is to query XML views of data irrespective of whether the 
physical data are in documents, SQL databases, OO repositories, or 
native XML databases.

> I must say that if that is indeed
> the goal, then it is doomed to failure. RDBMS, OO, and XML are three
> very different models and I don't think you can usefully combine
> them. 

Well, XML is a universal data meta-format; you can represent SQL, OO, 
and documentL data in XML, and XQuery lets you query that 
I didn't mean to imply that XQuery would let you unify the underlying 
data models.  It's true that you lose some of the relational model in 
an XML representation (the order of "rows" and "columns" becomes 
significant, and duplicates become allowed all of a sudden, and XQuery 
has to bend over backwards to allow these XML-isms to be ignored, as 
best I understand it).  Then again, the relational purists are always 
complaining that these aspects of the true relational model are ignored 
in many SQL database products, so I'm not sure that the practical 
significance of the impedence mismatch is all that profound.

I personally find this the most appealing aspect of XQuery -- I *want* 
to be able to do a join across an XML document collection and a table 
in an RDBMS, and maybe some topic map or RDF metadata thrown in for 
good measure.   But if you're right, it won't be the first time I've 
been cruelly disillusioned -- I've given up all hope that it will be a 
"small, easily implementable language" until it has had its butt 
whupped by Father Darwin a few times. <grin>


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