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Re: limits of the generic

• To: Jeni Tennison <jeni@j...>
• Subject: Re: limits of the generic
• From: Uche Ogbuji <uche.ogbuji@f...>
• Date: Sat, 28 Sep 2002 09:46:44 -0600
• Cc: Jonathan Robie <jonathan.robie@d...>, xml-dev@l...
• In-reply-to: Message from Jeni Tennison <jeni@j...> of "Sat, 28 Sep 2002 13:33:20 BST." <77163636536.20020928133320@j...>
• Sender: uche.ogbuji@f...

> Hi Jonathan,
> 
> > As for XPath, I think that the *lack* of datatypes made XPath 1.0 do
> > an awful lot of guessing, and in an attempt to keep things simple,
> > it said that ALL numbers are floating point numbers. I don't think
> > that the lack of datatypes in the data XPath 1.0 used made things
> > simpler or more straightforward, it led to baroque rules for
> > guessing types.
> 
> However baroque, it has to be said that the rules made XPath 1.0 very
> easy to use. It may seem baroque to implementers, who have to delve
> into the details, but to users XPath 1.0 appears to "just work". The
> same cannot be said of XPath 2.0.

It's neither baroque nor difficult for implementors either.  The part of XPath 
1.0 data typing that has the most coercion rules is the definition of 
EqualityExpression (i.e. interpretation of "=" and "!=".)  The entire 
implementation of this is less than 100 lines of Python code, and very clear 
Python code, I think.  In addition, about half of of this code is shared with 
the implementation of RelationalExpression.

I would guess that the equivalent implementation in XPath 2.0 would run well 
past 1000 lines of Python code.  This is just part of the reason why I don't 
plan to implement XPath 2.0.  The net gain for such staggering complexity is 
frightfully minimal.  Jonathan's examples, batting as hard as he can for data 
types, underscore this all too well.


-- 
Uche Ogbuji                                    Fourthought, Inc.
http://uche.ogbuji.net    http://4Suite.org    http://fourthought.com
Apache 2.0 API - http://www-106.ibm.com/developerworks/linux/library/l-apache/
Python&XML column: Tour of Python/XML - http://www.xml.com/pub/a/2002/09/18/py.
html
Python/Web Services column: xmlrpclib - http://www-106.ibm.com/developerworks/w
ebservices/library/ws-pyth10.html

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