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   RE: [xml-dev] RE: Incremental transformations with Xalan and performance

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 > Michael, you read a two years old version of the paper, the one I was pointing to is the journal
(i.e. longer) and newer version of it. The architectural main idea didn't change, but the numbers
are better (like any other new processor, the performance improves with 10% per day, so it depends
what day of the week do you measure ...:-) 
 I read the version I could find! Is it worth paying $35 to see the updated one? I did guess that your [BEA's!] numbers had almost certainly improved in the meantime (Saxon's figures on XMark are about ten times better than the ones you quoted).
By the way, the paper used a private benchmark to compare XQRL and Xalan-J, and suggested it would be available on the web. Is it? 

Our major goals while designing this were:
- build a full implementation for XQuery (I really mean 100%), not only a "convenient" subset
- use streaming
- use lazy evaluation

As you point out the interesting discussion is between pull and push streaming. There are multiple
reasons we used pull, the main important ones being:
- we are database people, so we grew up with the pull, iterator based evaluation of the relational
database engines and
- it was harder to make push and lazy evaluation work together  
In XSLT 1.0 it was relatively easy to use pull for the XPath reading, push for the XSLT writing. With the richer processing model of XQuery and XSLT 2.0 this mixed approach is certainly much more difficult. In Saxon today, many expressions can be evaluated in either pull or push mode, and the goal I'm pursuing is to keep both, while reducing the number of push/pull conflicts. The subject of a future paper perhaps.

There is a piece of good work that compares push and pull XML processing, I am sure you'll enjoy it. 
Well, it doesn't do much comparison, but it certainly makes a push-based approach look delightfully easy. If only it were true...
Michael Kay 

"The Joy of SAX" Leonidas Fegaras (University of Texas at Arlington, USA)

Best regards,

P.S. It looks like I am doing more publicity now to BEA, when I'm not there anymore:-)


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