[Zope3-dev] event service and channel

[Steve Alexander]

Jim Fulton wrote:
>
> I'll respond to both of these.  First, it is dogma that whether and how placeful
> services collabroate with services above them or with global services is a 
> policy/quality-of-service of the service implementation.
> 
> Second, Tres Seaver, who has a lot of experience with event systems feels strongly
> that there should never be more than one event service in a system and that, 
> therefore, it's a bad idea for any propigation to occur, at least among placeful
> services. 

Well, if there's never more than one placeful event service, it is 
merely irrelevant whether any event propagation occurs.

> I'm not sure I agree, but am willing to defer to his YAGNI for multiple
> nested placeful event services absent specific examples of cases where there there 
> is a  need for nested event services that isn't better handled by placeful 
> event channels.

I think the intent at present is to allow for nested placeful event 
services. A local event service has an on/off switch for whether it 
progagates its events to its parent event service, and an on/off switch 
for whether it subscribes to its parent event service.

I'd like to try out patterns using different arrangement of these 
switches. Perhaps there will be one true useful behaviour. Maybe many 
event channels and only one event service will serve most needs. In 
which case, we can apply a bit of yagni later on.

--
Steve Alexander