Re: [ Andrzej Jan Taramina ] [Embedlets-dev] Re: Event Manager

[Gregg G. W. <gr...@sk...>]

>The Embedlet Event Manager service will provide the ability for an event 
>consumer to specify criteria for the events they want to receive, and 
>this will include more than just the "type" of the event (since that is 
>pretty coarse grained).  
>
>You'll be able to subscribe to events by:
>
>	- event type
>	- producer (specific sender)
>	- various other properties (either user or system properties in the 
>       event).
>	- Any combination of the above.

The more complex you make the decision logic, the more overhead will be 
involved in
	1) executing the logic
	2) defining the interaction of the criteria (and, or, xor and not)
	3) educating users to use it correctly so that the documentation and
	   the implementations match.

We wanted to do all of these, and Jini LUS users want all of these.  But in 
the end, it is simpler to limit the criteria.  For pub/sub, I'd still suggest 
a simple hierachial topic string system, and that you should just include the 
appropriate parts in the topics.  Predefined topic trees would be beneficial, 
but using properties to configure modules to use the appropriate topic 
simplifies the whole mess by delaying this issue till deployment which can 
allow some modules to be used in ways that were not originally in the design.

control.switch.off.1.<producer>

is an example topic, where everything is specified.  In a topic system, at 
deployment time, you could match with

control.switch.*.1.*

to get all of switch 1 actions from all producers.  A single type of 
subscription, such as this, allows optimizations to be designed into the 
system, but letting presupplied topics to be 'compiled' to match optimally.  
When you include a more complex arrangement, such as an object that includes 
values for all of these, such as

new Event( SWITCH_CONTROL.ANY, 1, "*" )

you get a more complex system that is not very expandable, when the user 
actually has several other critera that they need to match on.

I do have a broadcast 'space' that includes single copy delivery in a mesh 
environment, and topic based pub/sub, that I am willing to 'donate' to the 
cause...

-----
gr...@cy...  (Cyte Technologies Inc)