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

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Daniela Florescu, Chris Hillery, Donald Kossmann, Paul Lucas, Fabio Riccardi, Till Westmann, Michael J. Carey, Arvind Sundararajan:
The BEA streaming XQuery processor.
VLDB Journal Volume 13, Number 3, September 2004

 An interesting paper.
(Funny how everyone uses Xalan-J as their baseline for performance comparisons - I wonder why?)
In the context of streaming, most of the techniques described are not very different from those used in the better XSLT processors. One big difference is that XSLT 1.0 is typically implemented using a dual push/pull model: XSLT instructions use a push pipeline to write a tree, while XPath expressions use a pull streaming model to read data from trees; whereas this paper describes a model that uses pull iterators uniformly. If you extend this all the way to using a pull parser to read the incoming XML data in the first place (and a pull-based streaming validator), then you do indeed get a system that avoids the need to construct the input document in memory, in the special (and probably rather unusual) case where all operations in the query have a fully streamed implementation.
(Note, however, that the push approach avoids the need to build the *result* document in memory, and in classic stylesheet applications, the result document is generally larger than the source document)
The conclusion of the paper is less than impressive "The running times can be improved... 3.8 MB is much larger that what the implementation of the engine was tuned for..." I'm seeing users doing XSLT transformations up to 200Mb, despite the limitation that the source document has to fit in memory! But nevertheless, the architecture looks very solid, and congratulations to BEA for publishing it, unlike vendors of "high-performance" XSLT engines who make marketing claims but give us no technical information to enable an informed assessment or comparison.
Michael Kay


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