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   RE: [xml-dev] Creating a Complex System using XSLT. Step 1: CreateFeedb

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The missing part of the amplifier analogy is one or several 
microphones/pickups that get that signal on output and route 
it back to the amplifier.  That alone produces the feedback. 
Something listens and routes.

To be more complete, because the environment (the room 
acoustics) shapes the signal, feedback can occur because 
the room is sensitive to a given frequency and reflects 
it back intensely.  One should look for both known couplers 
and surprise couplers.   Equalization is used to tune out 
the second kind (at the mics); the palm of the hand can be 
used to dampen feedback into the guitar pickup.  Also, 
mic grouping, mic choice (eg, SM57s are bad a bad sound 
but insensitive to feedback), and so on.

Given a pipeline (your supervisor) with multiple documents being dynamically

created and merged, one could indeed simulate feedback driven 
systems where the XSLT stylesheet acts as the filter (the 
equalizer) and the schema acts like the palm of a hand.


From: Thomas B. Passin [mailto:tpassin@comcast.net]

Roger L. Costello wrote:

> That leads me to another question - is feedback generally applied to the
> "data" or to the "process"?

Feedback is part of the processing of the data.  Think of an electronic 
amplifier.  The unmodified input signal is the data, the amplifier 
provides a transformation of that signal to create the output.  Thus, 
the stylesheet would be analogous to the amplifier (or other electronic 

With feedback, a part of the input signal is taken from the output.  If 
the feedback adds linearly to the input, and the feedback portion of the 
output is linear, the system is a lot easier to analyze than if there is 

Thinking about an xslt transformation, its functional design should 
prevent feeding back part of the output to the input.  Once the input 
has been read, it cannot be changed so far as the particular 
transformation is concerned.  Thus, xslt operates somewhat analgously 
(is that a word??) to an open loop amplifier.

So it would seem that to simulate fedback behavior using xslt, you would 
need some kind of supervisor sitting outside the stylesheet, capable of 
routing both its output and the original input to another 
transformation.  Could that supervisor also be a stylesheet?  I doubt it 
but maybe someone else could be clever enough.


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