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Re: Selector and Field XPaths (for Schema 1.1)

From: Stefan Wachter <Stefan.Wachter@gmx.de>
Date: Wed, 20 Nov 2002 16:34:44 +0100 (MET)
To: ht@cogsci.ed.ac.uk (Henry S. Thompson), xmlschema-dev@w3.org
Message-ID: <26941.1037806484@www23.gmx.net>

About 1:

I agree that the BNFs allow '.' and '//'. But the XPath
"self::node()/descendant-or-self::node()" is not covered by the wording in the spec.
 
The exact wording is:

"2.2 It must be an XPath expression involving the child axis whose
abbreviated form is as given above."

for selector XPaths and 

"2.2 It must be an XPath expression involving the child and/or attribute
axes whose abbreviated form is as given above."

for the field XPaths. These wordings should also mention the self and the
descendant-or-self axes.

About 2 and 3:

I thought it would be better to align the XPaths used in XMLSchema as much
as possible with the XPath 1.0 specification without increasing implementation
complexities too much and still fullfilling the requirement that only
descendants and their attributes are accessed.

--Stefan


> Stefan Wachter <Stefan.Wachter@gmx.de> writes:
> 
> > 1.
> > 
> > The spec. defines BNFs for the valid XPaths. However, it also states
> > (at 2.2) that XPaths whose abbreviated forms correspond to the BNFs
> > are also valid with the restriction that only the 'child' (and
> > 'attribute' axes in case of fields) are used.
> > 
> > Yet, the BNFs also use the 'self' and the 'descendant-or-self' axes.
> > Therefore I think that these axes should also be allowed for the
> > XPaths covered by (2.2).
> 
> 'self' is '.', which is allowed by the BNF, as is '//', which is
> descendant-or-self.
> 
> > 2.
> > 
> > The BNFs allow the '//', i.e. a 'descendant-or-self' step only at the
> > beginning. I think this restriction is not necessary because it does not
> ease
> > implementations and is conceptually not justified.
> 
> The restriction to one, initial, use of //, is intended to reduce
> implementation complexity for streaming implementations.
> 
> > 3. The 'descendant' axis should also be allowed.
> 
> What use case do you have in mind?
> 
> ht
> -- 
>   Henry S. Thompson, HCRC Language Technology Group, University of
> Edinburgh
>           W3C Fellow 1999--2002, part-time member of W3C Team
>      2 Buccleuch Place, Edinburgh EH8 9LW, SCOTLAND -- (44) 131 650-4440
> 	    Fax: (44) 131 650-4587, e-mail: ht@cogsci.ed.ac.uk
> 		     URL: http://www.ltg.ed.ac.uk/~ht/
>  [mail really from me _always_ has this .sig -- mail without it is forged
> spam]
> 
Received on Wednesday, 20 November 2002 10:35:16 GMT

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