XML tools and big documents (was: Re: Is there a size limitation on XML file given to MSXSL as input?)

David Megginson david at megginson.com
Tue Sep 1 23:03:51 BST 1998

Ingo Macherius writes:

 > > The problem comes if the parser tries to build a tree rather than
 > > simply reporting an event stream.
 > How many real world applications will be happy with just the event 
 > stream ? XSL-visualization always needs two trees, the parser tree 
 > and the resulting Formatting Object Tree (FOT). Double impact ! XML-
 > querys/DOM need to build a transformed versions. Triple impact !

Yes, but often the trees can be built and discarded at a fairly low
level.  For example, if I have a serialised database table like

    <name>David Megginson</name>
    <email>david at megginson.com</email>
    <name>Ingo Macherius</name>
    <email>macherius at darmstadt.gmd.de</email>
   <!-- etc., 2,500,000 times -->

I do not need to build a tree for the whole document; instead, I can
cache the information for each entry (or each n entries, for
efficiency), dump it into my SQL database (or whatever), then move on
to the next set.

The second situation is where you are using XML to serialise a data
model that is already well-defined (as for vector graphics).  In this
case, it makes more sense to build the specialised object tree
directly from the event stream rather than building a DOM tree only to
tear it down.  Specialised object trees can be considerably smaller
than a corresponding DOM tree, depending on the format.

All the best,


David Megginson                 david at megginson.com

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