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   RE: [xml-dev] XML Binary and Compression

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At 11:54 PM -0500 3/10/03, winkowski@mitre.org wrote:

>On reflection, I don't think that the conclusions reached are all that
>surprising. Redundancy based compression achieves better results as the file
>size, and consequently the amount of redundancy, increases. CODECS that take
>advantage of schema knowledge achieve efficient localized encodings and also
>need not transmit metadata since this information can be derived at decoding

I may have missed something in your paper then, because I didn't 
realize you were doing this. If you're assuming that the same schema 
is available for both compression and decompression, then you're 
doing a lossy compression. The conmpressed forms of your documents 
have less information in them than the uncompressed forms. I don't 
consider that to be a fair or useful comparison with  raw XML with 
metadata present.

Then again, maybe that's not what you meant? If you're somehow 
embedding a schema  in the document you transmit, then it's really 
just another way of compressing losslessly and that's OK, though In 
would still require that the schema used for compression be derived 
from the instance documents rather than applied pre facto under the 
assumption of document validity. Hmmm, that's not quite right. What I 
really mean is that given a certain schema it must be possible to 
losslessly encode both valid and invalid documents.

| Elliotte Rusty Harold | elharo@metalab.unc.edu | Writer/Programmer |
|           Processing XML with Java (Addison-Wesley, 2002)          |
|              http://www.cafeconleche.org/books/xmljava             |
| http://www.amazon.com/exec/obidos/ISBN%3D0201771861/cafeaulaitA  |
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