Implentation report update / OPTIONAL elements issue

Hi,

I've been preparing the implementation report [1]. Thanks to Tommy and
Yunhao and Guillermo for their feedback. Others are more than welcome to 
check it out and help complete it with their implementation experiences. Please
tell me if I put something in it you wouldn't want to see there. The @@
are the points I've not yet frozen.

Guillermo, could you tell me if we tested the HTTP bindings? I think we
only tested the SOAP ones, so I'm not sure how to report this.

I think that there is a real issue on how XKMS servers have to interpret
the OPTIONAL elements, and, in general, how these elements are to be
interpreted. It's not clear if OPTIONAL is being used here in the XML
Schema sense as an element or attribute that may appear or not in a 
message, rather than something that may or may not be supported by a 
client or a server.  This is ambiguous.

From the three points I got that required extra negotiations between
client and servers, two concern optional elements. In one of them Tommy
wrote 

<quote>
 If a server does not support the TimeInstant element, it should
indicate a failure *unless* it includes the optional ValidityInterval.
The danger being that if the client requests a TimeInstant and the
server does not support it.... 
</quote>

I think it's OK if a client doesn't support an element or decides to not
send it in a request if it's optional. A client may chose to ignore it
too. A server may decide to ignore it and do something different
following a given implementation policy. On the other hand, I feel that
it is wrong and that it is an interoperability problem if a server ignores
the element because it didn't implement it and does something
differently because the spec. said it was OPTIONAL and it didn't 
implement it.

What is your opinion about this? Do we need to add more text to the
spec. saying that servers should understand all OPTIONAL elements?

Thanks!

-jose

[1] http://www.w3.org/2001/XKMS/Drafts/test-suite/CR-XKMS-Summary.html
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