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From Christian Haul <>
Subject Re: Easy way to transformer parameters into a pipeline ??
Date Fri, 05 Sep 2003 15:22:53 GMT
On 05.Sep.2003 -- 04:54 PM, Lionel Crine wrote:
>  wrote:
> >Passing parameters down the pipe out-of-band (IOW by not adding a tag
> >that travels down the pipe in-band like the rest of the data) is a
> >dangerous thing as you have no idea about the actual
> >schedule. Usually, a SAX event callback is completely propagated down
> >the pipe before the next callback is invoked. However, by using
> >buffers one pipeline stage may complete before the next is started.
> I have a general idea of what you're talking about.
> Can you be more precise. How can I bufferize the stages ?

For one, Cocoon does it for you through the caching system. It can be
tuned in various way, still a component that issues data out-of-band
must not implement cachable for example.

Another opportunity to buffer the transformation is when debugging
your pipelines and write the result of a stage to a file....

> >So, you can use request attributes (or session attributes, an external
> >file, ...) to pass parameters out-of-band, provided it is not needed
> >for the following stage any earlier than the tag that causes the
> >parameter to be set.
> I didn't understand that.

naïve, but wrong:

 time     stage n      stage n+1
  0        <foo>
  1        <bar>
  2        </bar>
  3        </foo>------------------------sets parameter
  4                     <foo>------------needs parameter
  5                     <bar>
  6                     </bar>
  7                     </foo>

actual schedule:

 time     stage n      stage n+i

  0        <foo>
  1                     <foo>------------needs parameter, which parameter??
  2        <bar>
  3                     <bar>
  4        </bar>
  5                     </bar>
  6        </foo>------------------------sets parameter
  7                     </foo>



PS It would be nice if you could reply below the original message. It
makes it so much easier to follow an argument because you can just
read top to bottom.

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