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   Re: [xml-dev] Push and Pull?

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On Sun, Nov 25, 2001 at 02:17:08AM -0800, Dare Obasanjo wrote:
| the push model the API calls your methods as it sees parts of the
| XML stream while in the pull model you are in complete control of
| traversing the XML stream.
| One way of looking at it is that in the pull model, the big 
| while loop that iterates through all the nodes in document is 
| hidden from you while in pullmodel you're the one that writes it.


On Sun, Nov 25, 2001 at 01:44:33AM -0800, Dare Obasanjo wrote:
| From where I sit they are very different. Batch parsing is loading an entire
| stream or string into the DOM in one step with a loadXML or similar method,
| then interacting with the XML from the DOM. Pull parsing is at the other end
| of the horizon where you iterate through every node in your document
| one-by-one (text, element, PI, comment, etc) and perform operations utilizing
| the ones you are interested in.

I think you had it right the first time.  I'd define the push vs
pull distinction as a flow control issue (who owns the while
loop)?   The code with the while loop has an easier job since 
it can use the program stack to keep track of context.  The other
partner in the interaction must keep their state via some other
method (a call-back structure).  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.

Mixing access (random vs sequential) with flow control (push vs pull)
is how everything gets confused.   That said, sequential push and
random pull variants are the easiest to implement.  The sequential
pull seems the hardest to implement.   I've only just begun playing
with random access push models... this is more or less events that
can be revisited.


;) Clark

Clark C. Evans                   Axista, Inc.
http://www.axista.com            800.926.5525
XCOLLA Collaborative Project Management Software


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