Re: large XML files
On Mon, 8 Feb 2010, Lew wrote:
Lew wrote:
I know from a recent project that it's next to useless to match XPath
expressions with a SAX parser.
Tom Anderson wrote:
In what sense? That it justs builds a DOM tree behind the scenes?
In the sense that for XPath to work, there has to already be a DOM for
it to search, or else you have to forego built-in XPath processing.
Right, yes.
In that recent project they attempted to cache results from XPath
expressions that were built by manually matching the expression with
data from the streamed input. When that missed, they had to either
re-read the whole input or go ahead and build a DOM regardless. The
complexity and time cost of manual XPath handling and the frequency of
misses presented a rather intractable barrier to the approach.
Yes, unless you know what a large fraction of your XPaths are upfront, i
can't see that being a winning strategy.
That's only a single data point, of course. I don't rule out the
possibility that another approach to blending SAX and XPath could work.
Had it been up to me, I would have abandoned XPath for that application
and just used SAX or StAX to build a domain-specific object model, not a
DOM, and directly referenced items from that model.
Sounds sensible. Every time i've had to deal with XML and had the freedom
to do it how i liked, i've ended up doing just that - write a
ContentHandler that turns the elements into calls to some domain-space
interface, then write an implementation of that that either builds objects
or does something else useful.
tom
--
24-Hour Monkey-Vision!