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RE: XML Binary and Compression

• To: msc@m..., winkowski@m..., xml-dev@l...
• Subject: RE: XML Binary and Compression
• From: Elliotte Rusty Harold <elharo@m...>
• Date: Thu, 13 Mar 2003 10:45:47 -0500
• In-reply-to: <408A6ADBB8EBD511B27700508BB0CDE80A3EC7@l...>
• References: <408A6ADBB8EBD511B27700508BB0CDE80A3EC7@l...>

At 10:05 AM -0500 3/13/03, msc@m... wrote:
>I was thinking about this as well.
>
>If prefered, you could include some representation of the schema within the
>compressed format.  This would provide all the informatin needed for
>producing the orginal instance, assuming you know the proper algorithm.
>This would make things more like the tradtional gzip scenario, where the
>replacement dictionary is included in the compressed file, and it's assumed
>that you know the decoding algorithm.

There are some XML compression schemes that do this. I consider those 
non-lossy.

>The difference is that the schema based approach uses one set of information
>to encode/decode an entire class of instance documents.  Whereas in
>something like gzip, you need a custom-made replacement dictionary for each
>file you compress.  So in a schema based approach, you realy only need to
>deploy the schema once, rather than every time you send the compressed
>information.

This I don't believe. The fundamental flaw here is

1. Documents of interest have schemas
2. Documents of interest reliably satisfy their advertised schemas.

These flawed premises underlie a huge amount of XML theory. Neither 
of them matches XML practice. Any satisfactory compression scheme 
must be prepared to handle invalid documents losslessly.
-- 

+-----------------------+------------------------+-------------------+
| Elliotte Rusty Harold | elharo@m... | Writer/Programmer |
+-----------------------+------------------------+-------------------+
|           Processing XML with Java (Addison-Wesley, 2002)          |
|              http://www.cafeconleche.org/books/xmljava             |
| http://www.amazon.com/exec/obidos/ISBN%3D0201771861/cafeaulaitA  |
+----------------------------------+---------------------------------+
|  Read Cafe au Lait for Java News:  http://www.cafeaulait.org/      |
|  Read Cafe con Leche for XML News: http://www.cafeconleche.org/    |
+----------------------------------+---------------------------------+

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