Re: [xacml-comment] Non-deterministic output of the string-from-typefunctions

[Erik Rissanen <erik@axiomatics.com>]

Thanks again Steven,

I agree that it's a good idea to canonicalize as defined by the XSD spec.

I think we should just leave the LDAP DN form free. I doubt it is very 
useful to operate on the string form of in the first place.

Yes, it should say that the functions should evaluate to indeterminate 
if the input is not a valid lexical representation of the data type.

Best regards,
Erik


On 2011-03-29 07:02, Steven Legg wrote:
>
> Any given value in the value space of a non-string primitive data-type 
> has
> more than one valid lexical representation as a string of characters. The
> various string-from-type functions produce a lexical representation 
> for the
> value given as the argument to the function, but the descriptions of the
> string-from-type functions provide no guidance as to which lexical
> representation should be produced. This is an impediment to 
> interoperability
> when using these functions (particularly the string-from-double 
> function).
>
> For those data-types corresponding to XML Schema data-types, the 
> output of the
> string-from-type functions could be made consistent across 
> implementations
> by requiring that the canonical representation defined in "XML Schema 
> Part2:
> Datatypes" be used as the output.
>
> The other data-types are not so easy to canonicalize (for example, 
> there is
> no canonical form for an LDAP DN). However, given the currently available
> functions, any expression producing a value of one of these types is 
> ultimately
> just making a copy of one of the literal XACML attribute values that 
> was a
> direct or indirect input to that function, so a requirement on all 
> functions
> to preserve the original lexical representation of values of these 
> data-types
> may be an adequate solution. Note that this isn't suitable for the XML 
> Schema
> data-types. Consider the result of the double-multiply function, which 
> is an
> entirely new double value that is not equivalent to any of its input 
> arguments.
>
> On a related matter, the type-from-string function descriptions don't 
> say what
> to do if the input string is not a valid lexical representation for a 
> value
> of the output type. Presumably the function evaluates to indeterminate.
>
> Regards,
> Steven
>