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Subject: Re: [sca-assembly] Issue 227: what does promotion of channels meanwrt intents/policies

Hi Peter,

Not much time before the meeting to write a response, but here are some quick thoughts:

On 06/14/2010 06:50 PM, Peter Niblett wrote:
OF78C1CBA9.C55BC049-ON80257743.0006BD24-80257743.000A2472@uk.ibm.com" type="cite">
Hi Eric

I'm still having difficulty getting the right mental picture of what you mean by promoting a channel, but maybe it's just an artifact of the terminology we are using.  

Does seem to be some terminology question here, as "channel" by your definition sounds like it might be something different from what I'm thinking of.

OF78C1CBA9.C55BC049-ON80257743.0006BD24-80257743.000A2472@uk.ibm.com" type="cite">
I think I understand what it means to promote a service/reference or producer/consumer is promoted. This is because these things are "aspects" of a component, and therefore also aspects of a composite. So when you combine a set of components to produce a composite you can identify e.g. a reference or a consumer of the composite with the reference or consumer of one of the components contained in that composite.

On the other hand a channel is not an aspect of a component, instead it is a kind of peer to a component - it is a different kind of artefact that just does routing between real components. So you can't identify it directly with anything on the composite.  You could imagine promoting the producer or consumer aspects of a channel, so that they become producers and consumers of the composite (alongside any producers and consumers of components in the composite that were also promoted). That way any components in the composite that are connected to that channel stay using it, but other users of the composite have the ability to send events or receive events from that channel. However I don't think that's what you had in mind, since you wouldn't be able to tell that the promoted producer and consumer are attached to the same channel without peeking inside the composite definition.

Yes, this definitely highlights a terminology distinction.  For composability purposes, what I see is that the current model proposed for eventing allows me to couple a producer and consumer by way of the @target and @source attributes pointing at the same global domain channel.  If I have a way to couple the producer and consumer within a component type, then my concerns are quite diminished.  I can now couple them without reference to a domain channel, and thus have enhanced composability.

Now, I call that coupling a "channel", but that might be the terminology that is confusing you.  We could equally well call it "event-coupling", or "paired-eventing", or any other mangling.  In my head, that coupling is a logical reference to (not a definition of) an entity which could be a TIBCO Rendevous subject, or a JMS Topic, for example.

OF78C1CBA9.C55BC049-ON80257743.0006BD24-80257743.000A2472@uk.ibm.com" type="cite">

At the moment,  when constructing a composite, we say that you can
a) Connect components using a local channel. Such a channel is private to the composite and so not visible to anyone else
b) Connect them using a global channel. This isn't defined at all in the composite.. all the composite contains are references to it, but these references are hidden inside the composite definition and not visible at its externals.

So I think what you are asking for is a way to do
c) Connect them using a non-local channel. This isn't defined in the composite, but is given a kind of symbolic name. That name then becomes a property of the composite, and when an assembler creates the next higher composite they can either choose to map it to a real channel defined locally in that next higher composite, or map it to a global channel, or promote it up one more level.

I think you're pretty close here, but it is time to call in to the conf. call, so I'll wrap for now.


OF78C1CBA9.C55BC049-ON80257743.0006BD24-80257743.000A2472@uk.ibm.com" type="cite">

Peter Niblett
IBM Senior Technical Staff Member
Member of the IBM Academy of Technology
+44 1962 815055
+44 7825 657662 (mobile)

From: Eric Johnson <eric@tibco.com>
To: Anish Karmarkar <Anish.Karmarkar@oracle.com>, OASIS Assembly <sca-assembly@lists.oasis-open.org>
Date: 15/06/2010 00:48
Subject: Re: [sca-assembly] Issue 227: what does promotion of channels mean wrt intents/policies

Hi Anish,

Am I missing something here?

I don't see how this is any different from a service or reference that is promoted to the boundaries of a containing composite.

For that matter, the current eventing proposal promotes consumers and providers, and those in turn could be promoted to the boundary of the next containing composite.  The *only* difference I see is that my proposal leaves open the possibility that consumers and providers would be subject to the same policies set in the same place - for example an expectation of "confidentiality" set on a channel - and that seems more appropriate to me.

In any case, I don't see why you perceive that this question around policies is specific to channels.


On Jun 8, 2010, at 8:24 AM, Anish Karmarkar wrote:

> One of the things that has been proposed by Eric is promotion of channels outside of a composite. I'm assuming that such promotions will allow for intents/policies to be added on promoted channels by composites at higher levels. I'm not sure what that means to consumers/subscribers that are deeper down in the hierarchy.
> I imagine that channel policies/intents will impact all the consumers/producers connected to it. When a channel is promoted with additional/different intents/policies on it, what happens to consumers/producers that are connected to the same channel at a lower level. Are they affected by the additional intents/policies? If they are that would be very counter-intuitive. If they are not affected, is it still the same channel? For example, if it is a JMS topic, it is going to be the same topic for the consumers/producers at all levels. The topic has to be created with particular guarantees/persistence that are going to affect all consumers/producers. This changes the intent model. The intents would now flow up *and* down the hierarchy.
> -Anish
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