GetLastEventData() new elementary action

Emmanuel BEUQUE (ebeuque@pratique.fr)
Fri, 23 Jan 1998 10:24:30 +0100

À (At) 16:21 +0000 22/01/98, Xavier MARIE écrivait (wrote) :
>>> I only missed the first discussions of the MUG (I know I could check the
>>> archives) but I have never seen anything discussed about this
>>> GetLastEventData action to be added. Could it be possible to know in which
>>> area this issue needs further discussion, as stated in the WG12
>>> recommandations ?
>
>>Right, there was no discussions on the MUG concerning this event. As this
>>resolution states it is a recommendation from the MHEG ISO meeting in
>>Stockholm this summer. There were some discussions and it came up that this
>>actions might be a good solution. I can not remember what the actual subject
>>of the discussion was, can anybody of the participants help me with that?
>
>An Eventdata resident program was proposed by Andy Maxfield.
>This proposal was rejected (see MH_N1045) because getting
>the last event associated data would not only need an external program
>but also a change in the engine.
>Instead the functional requirement was therefore forwarded to the MTF.
>This is I think why "the issue needs further discussion"

Yes, in fact, the eventData is currently only used at the time the engine
check all active links against a newly generated event. The
GetLastEventData would require to have it available at the time of the
execution of the LinkEffect when a link is fired.

I understand that this may be a problem for an engine. While an event is
only generated at a time and checked immediately, several link effects
could have been added to the execution queue, E.G. a link effect action can
fire another link.

I think that programmers of engine would consequently ask for some
restrictions, for instance, the following one :

"GetLastEventData only returns the eventData associated with the last
generated event. It should generally be called as the first elementary
action of the linkEffect in order to prevent other link to be fired before
its evaluation. The author should also be aware of possible side effects if
several links may fire on the same event."

That means that an author could not be sure to get the eventData associated
with the current link when evaluating GetLastEventData in the linkEffect.
This would be erroneous if another event was generated after the link fired
but before the action is evaluated.
I don't think that the EventData type could be a problem. Some other
elementary actions use several types such as SetVariable for instance.

Any opinion ?

BR,
Emmanuel

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Emmanuel BEUQUE mailto:ebeuque@pratique.fr
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