Re: [xacml-users] xpath access control

[Argyn <jawabean@gmail.com>]

On 11/30/06, Anne Anderson - Sun Microsystems <Anne.Anderson@sun.com> wrote:
> Argyn,
>
> [I haven't checked my XPath syntax below, but I hope the idea is clear.]

yes, that's the question: what is exactly "semantical equivalence".

>
> As an example of the problem, does /A/B[@x="5"]/C
> select the same nodeset as /A/B[2]/C ?

i'd say that these expressions are not semantically equal.
semantically equal expressions should return the same results on the
same input, imho. in your example XML, /A/B[2]/C and /A/B[1+1]/C xpath
expressions would be such. they are syntaxically different, but do the
same thing

> The only solution to this problem is limiting your XPath expression
> syntax such that any two expressions select the same nodeset if and only
> if the expressions are syntactically equivalent.  I have no proof, but I
> hypothesize that it is sufficient to require absolute expressions, and
> disallow query operators and element order specifiers.

in my example, both are sort of absolute expressions, but they are
syntaxically different, making it harder to match them with regexp

thanks.
argyn