Re: XPath grammar questions

> The first case is in a path submitted by Tobias Reif, that originated, as
I
> recall, from someone on this list:
>
>  *[* and not(*/node()) and not(*[not(@style)]) and not(*/@style !=
*/@style)]
>
> Specifically, it's the 'not(*/node())' that I'm having trouble with.  The

> XPath spec states that:
>
>   not( boolean ) -> boolean
>
> This would imply that '*/node()' evaluates to a boolean.  However, it
also
> states that paths such as:
>
>   ancestor::node()
>
> evaluates to a set of matching nodes.  Further, I had assumed that the
path:
>
>   */node()
>
> by itself would also result in a set of nodes.
>
> I have a group of theories about this, but I'm not quite grokking the
intent
> of XPath.  I don't see how the same path should evaluate to two different

> results.  In any case, there have been a number of successful
implementations
> of XPath, so I know I'm missing something.

The rules for conversion are spelled out in the XPath recommendation,
although can get prettty convoluted.  In this case, an empty node-set is
converted to the boolean value false, while a non-empty node-set is
converted to the boolean value true.

> The second (and at this point, more critical) problem I'm having is with
> function names.  Take:
>
>   [normalize-space(@name)='x']
>
> If you follow the grammar, the evaluation is:
>
>    Predicate->Expr->OrExpr->AndExpr->EqualityExpr->RelationalExpr->
>    AdditiveExpr
>
> at which point it matches the rule:
>
>   AdditiveExpr:: AdditiveExpr '-' MultiplicativeExpr

> where you effectively have "normalize" "-" "space(@name)='x'".

Your tokenization is incorrect -- normalize-space is one token. See:

   http://www.w3.org/TR/xpath#exprlex

In particular:

   "When tokenizing, the longest possible token is always returned"

Also, see:

   http://www.w3.org/TR/xpath#numbers

   "The - operator performs subtraction.

   NOTE: Since XML allows - in names, the - operator typically needs to be
   preceded by whitespace. For example, foo-bar evaluates to a node-set
   containing the child elements named foo-bar; foo - bar evaluates to the
   difference of the result of converting the string-value of the first foo
   child element to a number and the result of converting the string-value
   of the first bar child to a number."

Dave



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