Re: [sca-assembly] Issue 227: what does promotion of channels mean wrtintents/policies

[Peter Niblett <peter_niblett@uk.ibm.com>]

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.  

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.

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.

Regards

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

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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.

Eric.

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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