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Subject: RE: [sca-assembly] SCA Eventing Pub/Sub Contribution FAQ


 

 

From: Estefan, Jeff A (3100) [mailto:jeffrey.a.estefan@jpl.nasa.gov]
Sent: 04 September 2009 18:17
To: 'OASIS Assembly'
Subject: RE: [sca-assembly] SCA Eventing Pub/Sub Contribution FAQ

 

Martin et al.,

 

Frankly, I’ve been tracking this thread for a while and I don’t get all the fuss around trying to add event processing capability to a services paradigm programming model.  With the exception of insuring that the SCA programming model can support multiple message exchange patterns (MEPs) for service invocation and alternative response (whether it be support for asynchronous queuing, request/response, request/callback, request/polling, batch processing, or, more to the point, “event-driven” pub/sub), why are we attempting to add support in SCA for the event processing paradigm in general?  It’s not a service-oriented paradigm; in other words, it is not capability- or functionally-driven at its core.

 

[<MartinC>] In our experience, its very hard for an application or sub-set of an application to fall neatly and exclusively into one of a client/server or a pub/sub  paradigm. In general, a mix of both is required to build complex applications. The heart of SCA, IMHO, is the component nature of the model and if one acknowledges that a component may offer or use services, and/or may generate or consume events, then we need a way to describe and configure these facets.

 

It would seem to me that we would only need to insure that that SCA-Assembly spec support the notion that some entity that, upon occurrence of certain events of interest, triggers the invocation of a service.  In that way, such an entity would simply be another SCA client and communication between the consumer/client and provider entity (service) could be any of the supported MEPs.

 

[<MartinC>] We tried to build support in such a way, but we found the client/server and pub/sub paradigms to be too different to fit one on top of the other.

 

So my point is, why not add an entry to the eventing pub/sub FAQ list  that questions the support for event processing at all?

 

[<MartinC>] What would the question be?

 

This is in contrast to the current list of FAQs, which focus on the assumption that such support is required and what needs to be changed in the SCA programming model to support it.

 

As an aside, I would like to participate in your Wed discussions on this topic but it conflicts with another TC meeting I have.  I’ll do my best to follow the thread and respond accordingly.

 

Regards…

 

 - Jeff E., NASA/JPL



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