Re: [wsn] Preconditions

[Peter Niblett <peter_niblett@uk.ibm.com>]

Susan's original question was in effect "is the precondition something that
is evaluated just once, when the the subscribe request is being processed;
or is it something that is (logically) reevaluated each time the NP has a
message to send?"  You could go further and ask "if the NotificationMessage
is sent to n consumers, does it get evaluated n times or only once?"

The syntax and semantics of a precondition aren't defined by
WS-BaseNotification - they are defined by the Dialect URI, so we could say
that the question of when/how often it is evaluated is determined by the
Dialect itself.

However I think that it is reasonable for BaseNotification to mandate that
a precondition is evaluated once each time the NP has a message to send. In
the case where the precondition has no side-effects, then an NP could
choose to optimise this, and not actually execute the expression if it
knows that nothing has changed.

The other example

Peter Niblett



                                                                           
             David Hull                                                    
             <dmh@tibco.com>                                               
                                                                        To 
             05/11/2004 14:54          Susan Malaika <malaika@us.ibm.com>  
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                                       wsn@lists.oasis-open.org            
                                                                   Subject 
                                       Re: [wsn] Preconditions             
                                                                           
                                                                           
                                                                           
                                                                           
                                                                           
                                                                           




Susan Malaika wrote:


      Should the time of evaluation of preconditions go into the
      specification or be left open to interpretation?


If there's more than one reasonable way to do it, either should be allowed,
and it should be possible to advertise which behavior is implemented.  In
other words, we have just turned up another parameter/policy/whatever.



      Susan Malaika






      To: Susan Malaika/Santa Teresa/IBM@IBMUS, wsn@lists.oasis-open.org
      cc:
      Subject: RE: [wsn] Preconditions




      It's the latter, as I understand.

      I guess the notification may not even be produced as a result of
      evaluating a precondition. For example, if  precondition is
      debug=true, and the Producer is not in a debug mode.

      Thanks,
      Sanjay
      -----Original Message-----
      From: Susan Malaika [mailto:malaika@us.ibm.com]
      Sent: Thursday, Nov 04, 2004 4:36 AM
      To: wsn@lists.oasis-open.org
      Subject: [wsn] Preconditions




      When are preconditions evaluated? When a subscription is made? When a
      notification is about to be produced?

      Susan Malaika