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Re: XML-enabled databases, XQuery APIs

• To: david.lyon@c...
• Subject: Re: XML-enabled databases, XQuery APIs
• From: David Carlisle <davidc@n...>
• Date: Tue, 19 Apr 2005 10:47:07 +0100
• Cc: xml-dev@l...
• In-reply-to: <200504191931.10692.david.lyon@c...> (message fromDavid Lyon on Tue, 19 Apr 2005 19:31:10 +1000)
• References: <200504181843.j3IIhFvI097554@w...> <42649218.5010404@r...> <001301c544b3$a25a5170$1601a8c0@DURANTE> <200504191931.10692.david.lyon@c...>

  One point I would like to make is from the python link 
  (http://www.oreillynet.com/pub/wlg/6291) where mention
  is made to the assumption of parsing 8-bit text documents 
  when Unicode docs may be the norm in the future.

Unicode encodings are already the default encodings in windows and more
recent linux distributions, so that would be now, not "in the future".

  Unicode is (according to my understanding) an 8-bit escaping system. That is 
  if the character is extended, it is written into a second, third and then 
  consecutive bytes if required.


No, That is (more or less) a description of UTF-8. Unicode itself has
nothing to do with bytes or encodings, it is a mapping of a set
of characters (with associated names and other properties) to numbers in
the range hex 1 to 10FFFF.

> So to do really *fast* unicode stuff, ideally, the in-memory view wouldn't 
> store the characters in 8-bit, but just as 32-bit (4 byte) or 64-bit (8 byte) 
> strings.

That would be UCS4 encoding (otherwise known as utf-32)

http://www.google.co.uk/search?q=UCS4

utf-16 is also common, probably more so than utf-8 (java uses utf-16 by
default as does msxml).

David

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