From: Marc Hoeppner <marc.hoeppner@...>
Date: 2008-01-13T01:58:08+09:00
Subject: Stream Parsing with REXML

Hi (again, sort of) :)

I am still on my quest to write a program that parses a large XML file.
After having tried to do it in tree mode, I had to realize that the
performance was simply abysmal. So back to the drawing board. But, and
here is the thing...I could find a good straight-forward tutorial on how
to write a stream parser using REXML. The official tutorial is pretty
much mute on that part and the only other example I found (or rather was
pointed to -
http://www.janvereecken.com/2007/4/11/event-driven-xml-parser-in-ruby)
was way too complex for someone like me who is still pretty much a
beginner in ruby.

So, what I am looking for is either a brief description of how to write
an event driven parser or else a link to a good and simple tutorial.

For the former, this is what the parser should do:

Find the element "Gene-ref", allow me to access its children and then
close and repeat for the next "Gene-ref entry. In xml code, that would
look like

<something here>
 <Gene-ref>
  <name>...</name>
  <start>...</start>
  <end>...</end>
 </Gen-ref>
 <Gen-ref>
 ...

I understand that I need a Listener class, like
classListener
  def tag_start(name, attrs)
  end
  def text(text)
  end
  def tag_end(name)
  end
end

But I havent really worked with classes all that much and maybe someone
could just put down the basics for the script from where I can start
experimenting? Would be very much appreciated. Let's say for each
element "Gene-ref" I want to puts the name, start and end in one line,
or something along those lines.

Cheers,

Marc
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