attribute exchange value encoding

[Claus Färber]

Johnny Bufu schrieb:
> The attribute metadata can be used to define attribute-specific  
> encodings, which should deal with issues like this.

Ah, so the _usual_ way is that the metadata (Can this be renamed to 
"datatype definition"? "metadata" is very misleading.) defines the 
encoding. For binary data, it will be base64Binary or hexBinary as 
defined in XML schema. Correct?

> The AX protocol has to stay simple (that was overwhelming feedback  
> I've received at IIW). The base64 encoding is there as a convenience:  
> if a number of OPs and RPs agree on an attribute type (the classical  
> example being an avatar image) but don't want to go to the trouble of  
> publishing metadata information,

In other words: The metadata is implicitly agreed upon by the parties 
involved. If they can agree on the meaning and the base format (integer, 
string, *binary,...) they can also agree on an encoding (e.g. agree on 
base64Binary instead of *binary).

So I don't think AX needs means to flag base64 data. The parties 
involved should know when base64Binary or hexBinary is used by out of 
band information (metadata/datatype definition or mutual agreement).

In other words, AX should just restrict values to UTF-8 strings and 
recommend base64Binary (or hexBinary) for datatypes (datatypes, not 
data!) that can't be represented as UTF-8 strings.

Claus