[gme-users] Constraint problem

[Larry Howard]

Thanks Jeff, this helps clarify my proposal.
 
I propose instead the ability to say that a constraint should be checked
exclusively on the associated events.  
 
I think that this would put things nicely into the hands of the
meta-modeler.

-----Original Message-----
From: gme-users-bounces at list.isis.vanderbilt.edu
[mailto:gme-users-bounces at list.isis.vanderbilt.edu] On Behalf Of Jeff
Parsons
Sent: Thursday, March 02, 2006 10:56 AM
To: gme-users
Subject: RE: [gme-users] Constraint problem


What about the case where GME is used with other tools, for example one that
generates
XML for GME to import. If this tool had a bug and generated something that
violated the
constraint in question, wouldn't "Check All" be the only way to catch it?


  _____  

From: gme-users-bounces at list.isis.vanderbilt.edu
[mailto:gme-users-bounces at list.isis.vanderbilt.edu] On Behalf Of Larry H.
Sent: Thursday, March 02, 2006 10:32 AM
To: gme-users
Subject: [gme-users] Constraint problem


I'm having a problem defining a constraint that concerns a change in number
of children in a container.  My intention is to check this constraint on an
event, like "onlostchild", and to prevent the action by setting the
constraint's Priority=1.  My problem is to find an approach that does not
subsequently trigger a violation when the user chooses the 'Check All'
action of the Constraint Manager.
 
It is my current belief that there is no way to define such a constraint.
The reason is that the focus of this constraint is "change", whereas the
focus of the Constraint Manager, in general, is "current state".
Constraints concerning "change" typically involve knowing "state before" and
"state after".  Have I failed to consider something?
 
One thing that occurs to me is that the Constraint Manager might consider
not checking constraints on "Check All" that are checked on events with
Priority=1.  The intuition is that, since such event-based constraints can
only result in aborting the action, there is simply no reason to check them
again on "Check All".  Such a feature would allow the desired constraint to
be defined quite simply with a "false" predicate.
 

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