[graap-wg] updated draft - symmetry

[Karl Czajkowski]

On Apr 05, Jon MacLaren loaded a tape reading:
...
> What kind of obligations can you have on the initiator side if "the 
> obligations in the agreement are not dependent on the initiator being 
> informed of the decision"?
> 
> I can't reconcile these two ideas.
> 
> Jon.

The point is that there is a momentary hazard where the initiator is
_possibly_ obligated and does not know whether the Agreement will
happen or not.  If he is obligated to pay for service, he doesn't know
whether he will need to present funds at some point... he might not
want to spend them elsewhere, etc.

In many cases, this hazard can be dealt with speculatively: by waiting
for the answer.  Waiting is not a satisfactory speculative behavior if
and only if the Agreement terms include real-time scheduling
constraints at the same temporal granularity as the messaging, e.g. if
waiting causes a violation.

This is a theoretical corner case, and may not be a practical one if
entities are conservative about the kinds of agreements they will
negotiate, e.g. not trying to negotiate about services with hard start
times that are "too close" to the present. Another solution might be
to deploy WS-Agreement in an environment with better messaging
guarantees.  If messaging itself were trustworthy, it might make sense
for there to be introspective terms in the Agreement that bound the
responder's decision time (for example, the responder is in violation
if he says "yes" too late). For many best effort cases, the waiting
solution can mask this hazard since delay is not a violation for
either party.

I really don't know where to go with this discussion.  I've been
making this point for years too... A phased approach cannot resolve
this hazard: someone is always the last to know, and the other party
doesn't know if he knows.  Pure transactions do not work in this kind
of quasi-realtime problem where they cannot be rolled back, i.e. work
cannot be undone and resources cannot be unspent.  Other compensation
actions must be undertaken, e.g. pay a penalty, to offset the costs of
the system thrashing and not doing real work.


karl

-- 
Karl Czajkowski
karlcz at univa.com