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   Annotations in XPath-NG? (Re: [xml-dev] XPath/XSLT 2.0 concerns)

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> > In an ideal world, XPath 1.0 could be one of these modules!
> Yes, or at least something that looks so darned close to XPath 1.0
> that no one would know the difference. I do think that the underlying
> data model from XPath 1.0 needs to change a little, to support a "type
> annotation" feature, make it closer to the Infoset and all that, but
> what I'd like is for it to be much more agnostic about where that
> typing information comes from and what the types are (the types are
> just labels).

I think one could imagine a lot of what would be added/tweaked in XPath 1.0 
for a killer 2.0.  I agree that an annotation system would be great for XPath 
2.0, and, in fact, Eric and I had been discussing how to add such a thing to 
4Suite so we could implement some of the modular data typing straw men we've 
been discussing.

My foirst comment is that it should be generic annotation, not just type 
annotation.  My thoughts would be:

Add an "annotation" property to each node.  This is a simple key/value pair 
where the key is URI (or is that anathema  ;-) ) and the value is any XPath 
1.0 object (which would even allow annotations to be cross-node links).

You can access any particular annotation for any particular XPath object with 
a function lookup(annoitation-key).  Of course, some facilities, such as 
optimizers, might use annotations behind the scenes, directly.

Does this sound like a good general approach?

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.
Python/Web Services column: xmlrpclib - http://www-106.ibm.com/developerworks/w


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