All,
In issue 88 it has been proposed that all functions from XPath 2.0 be
made available in XACML by means of a general mechanism.
I have looked at this issue and it seems to be doable.
Function calls in XPath 2 are defined here:
http://www.w3.org/TR/xpath20/#id-function-calls
In short, the call is written as a qname followed by its arguments. Such
as this:
my:three-argument-function(1, 2, 3)
It would be simple to define some form of syntax which means that a
particular XPath function is evaluated. It could naturally be done in a
number of different ways.
The XPath 2 function library is defined here:
http://www.w3.org/TR/xquery-operators/
Potential issues I see:
- Do all the functions and data types make sense to XACML?
For instance, there is function called fn:node-name which returns the
name of a DOM node. Would including this function and its associated
data types make sense in XACML?
Another one is fn:error which raises an error. (BTW, some form of error
raising capability would be good to have in XACML, for instance to make
assertions about expected attributes in the request.)
Perhaps we should enumerate a list of functions and data types which we
think make sense?
- XPath does some type conversion to function arguments. Are we
comfortable with this, considering that XACML has been strictly typed?
- Are we happy with qnames as identifiers? Traditionally XACML has not
done that. Perhaps we could create URIs from the qnames using
namespace#name such as done in the XMLSchema data types. For instance
http://www.w3.org/2005/xpath-functions#upper-case would convert a string
to upper case. I searched the spec for a convention like this, but I
couldn't find one, so we should probably not make up one.
BTW, the daytime and yearmonth durations are defined in the "op:"
namespace. This namespace does not have a definition and the functions
are not intended to be callable by users. Sadly, I was hoping that we
would get our new function identifiers for the duration functions from
the xpath spec.
So, assuming that we can go with qnames, we could do something like this:
(Alternatively we could overload the regular
