Fw: Last Call Issue: CHOICE WITH MIXTURE OF BLOCKING AND NON-BLOCKING ELEMENTS

----- Original Message ----- 
From: Gary Brown 
To: public-ws-chor@w3.org 
Sent: Wednesday, January 05, 2005 2:21 PM
Subject: Last Call Issue: CHOICE WITH MIXTURE OF BLOCKING AND NON-BLOCKING ELEMENTS


If a choice construct has a mixture of blocking and non-blocking elements, then it is not clear how these should be processed.

"If the choice has Work Units with guard conditions, the first Work Unit that matches the guard condition is selected and the other Work Units are disabled."

Does this mean the 'first' with respect to time, or the first in lexical order?

For example, if the choice construct has two elements, the first one blocks awaiting some information, while the second element is non-blocking:

- should the choice construct evaluate the first item and then suspend until the first element has a known value.

- or should the blocking element be skipped as its value cannot be determined, and therefore the second element is evaluated?

However, if this second element evaluates to false, then does this mean that the choice suspends awaiting one of the blocked elements (i.e. the first element in this case) to be evaluated to true, or until no elements remain to be evaluated?

The semantics of the choice construct are unclear in this situation.

Regards

Gary and Steve