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RE: Push and Pull?

• To: 'Nicolas Lehuen' <nicolas.lehuen@u...>, "'Clark C . Evans'" <cce@c...>
• Subject: RE: Push and Pull?
• From: "Sterin, Ilya" <Isterin@c...>
• Date: Fri, 25 Jan 2002 18:16:50 -0800
• Cc: xml-dev@l...
• Importance: Normal
• In-reply-to: <008f01c1a5ed$97a01ed0$0100000a@nico>

Just wondering, the ability to switch from sequential to random access,
still will allow the parser to reparse, unless there is a way to specify
the nodes to keep before the actual parsing begins.  It seems as if
dom4j is actually just a combination of both separate interfaces, but
doesn't actually allow to use them simultaneously.

Ilya

> -----Original Message-----
> From: Nicolas Lehuen [mailto:nicolas.lehuen@u...] 
> Sent: Friday, January 25, 2002 2:14 PM
> To: Clark C . Evans; Sterin, Ilya
> Cc: xml-dev@l...
> Subject: Re:  Push and Pull?
> 
> 
> SAXDOMIX [1] could be classified as semi-random-access, 
> push-flow-control-interface. It enables you to parse a 
> document in the SAX model, and switch when desired to the DOM 
> model to build partial trees that are pushed into a 
> controller. It is semi-random access because you have full 
> random access on the partial trees, but sequential access 
> between them.
> 
> dom4j also implements this idea, in a less generic way (but 
> much more simple and easy to use), and calls it 'tree pruning' [2].
> 
> This approach is quite interesting for XML document with a 
> fixed-depth repetitive structure, such as a list of elements 
> with a complex structure. It simplifies your code by making 
> it possible to use tree accessors (imagine how it would be 
> great with dom4j XPath accessors !), instead of having to 
> deal with a stack and/or a state-machine, without forcing the 
> whole document to be loaded in memory.
> 
> Regards,
> Nicolas
> 
> 
> [1] http://www.devsphere.com/xml/saxdomix/
> [2] 
> http://dom4j.org/faq.html#How%20does%20dom4j%20handle%20very%2
> 0large%20XML%2
> 0documents?
> 
> N.B. the anchor contains a '?', so the link is not valid in 
> Outlook Express. Sigh.
> 
> ----- Original Message -----
> From: "Clark C . Evans" <cce@c...>
> To: "Sterin, Ilya" <Isterin@c...>
> Cc: <xml-dev@l...>
> Sent: Friday, January 25, 2002 8:01 PM
> Subject: Re:  Push and Pull?
> 
> 
> > On Fri, Jan 25, 2002 at 11:29:51AM -0700, Sterin, Ilya wrote:
> > | >In SAX, the parser is has the
> > | >control loop and thus this makes SAX parsers easy to 
> write.  In DOM 
> > | >the control loop is owned by the library's user.
> > |
> > | That said, it again brings us down to that SAX parsers all (most) 
> > | follow the push model, and DOM based follow the pull model.
> >
> > DOM [1] uses a random-access,     pull-flow-control interface.
> > SAX [2] uses a sequential-access, push-flow-control 
> interface. XPP [3] 
> > uses a sequential-access, pull-flow-control interface.
> >
> > | > I've only just begun playing with random access push models... 
> > | > this is more or less events that can be replayed
> > |
> > | For the push model to be replayed, probably means that it 
> will have 
> > | to keep a parts in memory, or reparse all over again?
> >
> > Yes.  To offer random access an interface will probably 
> elect to keep 
> > an in-memory representation.  Although a random access 
> interface could 
> > be done over a database (see Tamino), etc.
> >
> > | This means that we are back to in memory parsers right, 
> or is there 
> > | some other concept behind it?
> >
> > Right.  The examples above give you 3 permutations, one
> > could develop an interface which used random-access but 
> > push-flow-control.  I started to put together an interface for this 
> > about a year back... it had a way for events
> > to be "re-played".   I stopped after I didn't see an
> > obvious application of the technique.
> >
> > ;) Clark
> >
> > [1] http://www.w3.org/DOM/
> > [2] http://www.saxproject.org/
> > [1] http://www.extreme.indiana.edu/soap/xpp/
> >
> > --
> > Clark C. Evans                   Axista, Inc.
> > http://www.axista.com            800.926.5525
> > XCOLLA Collaborative Project Management Software
> >
> > -----------------------------------------------------------------
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> 

• References:
  • Re: Push and Pull?
    • From: "Nicolas Lehuen" <nicolas.lehuen@u...>

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