[xquery-talk] RE: [AW] XQuery and Item Orientation

Ghislain Fourny gfourny at inf.ethz.ch
Sat Jan 24 20:39:51 PST 2009


I think that it is an important point that the relevance of object- 
orientation features in XQuery depends on the use cases. Everybody (I  
think) agrees that XQuery is very efficient and well-suited to process  
XML/relational data: it was designed exactly for this. The question  
here seems to be: can XQuery do more, e.g., do what Java/C++ do --  
without reducing performance on pure XML processing -- and would this  
be desirable at all?

My feeling is that XQuery has a considerable potential. As Hans- 
Juergen Rennau mentioned it earlier, XQuery/XML/XPath was one of two  
major revolutions in software development, the other being object- 
oriented programming, and so I am also wondering: would it not be nice  
and useful if one were able to design a seamless (i.e., XML nodes and  
objects are "the same") solution cumulating the best sides of both XML  
Querying and Object-orientation in a single language? Would not XQuery  
be a good match for this?

The mapping suggested by Hans-Juergen Rennau following Michael Kay's  
comment about patterns with user-defined priority (as an alternative  
to type hierarchies for polymorphism) is interesting. I have questions  
regarding this: with this approach, what kind of control would an  
implementor/a user have about which function is called when? How would  
this affect predictability of program execution and debugging? Does  
XQuery not already have some kind of type-hierarchy-based polymorphism  
(the recommendation says in 3.1.5. (Function Calls) "the rules for  
SequenceType Matching permit a value of a derived type to be  
substituted for a value of its base type")?

Kind regards and thanks a lot for your interesting comments,
Ghislain Fourny

> I think it is a question, about which use cases we talk: on a database
> I do not need these features. But in application programming, this
> would make a lot of sense. Writing a web application in Unity seems to
> me to be more comfortable than in XQuery.
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