Re: [sca-assembly] Misadventures exploring "@coupledTo" for proposedresolution of ASSEMBLY-227

[Mike Edwards <mike_edwards@uk.ibm.com>]

Folks,

I find it VERY hard to see how this
"double headed beast" termed "prosumer" (or use whatever
other term you find more congenial) is
in any way simpler or avoiding of the
problems laid at the door of either "groupID" or "coupledTo".

The trouble with "prosumer"
is that I think it ends up having to include all the features and capabilities
of both a producer and a consumer,
with the need for both @target and @source
- and also allowing for promotion (and in the worst case allowing for promotion
to a 
prosumer, to a consumer & to a producer).
 AND the rule has to be that some combination of these things ensures
that there is a "path"
that connects the prosumer to itself
via some channel.

To avoid those problems, you end up
having to place restrictions on what a prosumer can do - and any such restrictions
are equally
applicable to "groupID" or
"coupledTo" (etc).


As for avoiding the notion of a producer
explicitly naming a consumer - that IS the game we are in here.  You
can't hide it, no matter
how you try.  For sure, the producer
and the consumer involved may be connected via some (as yet unspecified)
channel, but the
fact of them BEING connected to one
another IS the point of this function.


You want simplicity?  Then don't
have this "this producer must be connected to this consumer"
type of function in the model at all.
Clearly an Assembler can achieve this
function if they so wish - it's a piece of cake for the assembler.  It's
just that putting this metadata
into the model in a way that it can
be POLICED by the runtime (or by tooling) is what generates all this complexity.
 Leave it as
descriptive metadata in the implementations/composites.
 Job done.

Yours, Mike

Dr Mike Edwards		Mail Point 146, Hursley Park
STSM		Winchester, Hants SO21 2JN
SCA & Services Standards		United Kingdom
Co-Chair OASIS SCA Assembly TC
IBM Software Group
Phone:	+44-1962 818014
Mobile:	+44-7802-467431 (274097)
e-mail:	mike_edwards@uk.ibm.com

From:	Eric Johnson <eric@tibco.com>
To:	Anish Karmarkar <Anish.Karmarkar@oracle.com>
Cc:	sca-assembly@lists.oasis-open.org
Date:	07/12/2010 00:11
Subject:	Re: [sca-assembly] Misadventures exploring "@coupledTo" for proposed resolution of ASSEMBLY-227

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Hi Anish,

On 12/6/10 3:57 PM, Anish Karmarkar wrote:
> I think this is fine.
> Although, I do find the minimal change to CTs via Mike's proposal
> attractive. But certainly understand the complications that come with
> it wrt policy/intent and constrains like everything has to be promoted
> or connected.
>
> A minor difference, perhaps inconsequential at this stage is, wrt
how 
> I envisioned Mike's proposal to work:
> I didn't think of a @mustConnectTo or @coupledTo as the attribute
we 
> would use but an attribute such as @label or @groupID, which would
be 
> any arbitrary string. The @mustConnectTo or @coupledTo identified
> other consumers (or producers). I would rather the producers not point
> to consumers (or vice versa). Instead, the producers and consumers
> that are to be connected together would be identified with a common
> label/group id.

In one of the later emails, Mike and I discussed the problems with a 
generic label, and I think we both agreed that a "groupID" kind
of 
notion allowed for an extra axis of flexibility (promoting to two 
consumers on the composite, for example, but assigning the same group 
ID) that isn't required by the use case, and simply introduces an extra
opportunity for confusion and mis-wiring.  So we had agreed on 
@mustConnectTo in the email referenced below (00100).

-Eric.

>
> -Anish
> -- 
>
>
> On 11/30/2010 1:47 PM, Eric Johnson wrote:
>>   As per my action item, I've been trying to write up the
approach that
>> I agreed to, the one that Mike suggested:
>>
>> http://lists.oasis-open.org/archives/sca-assembly/201011/msg00100.html
>>
>> Mike labeled this as "@mustConnectTo" in his proposal,
but I thought it
>> more natural to call this "@coupledTo".
>>
>> Rather than spell out the changes I was making, let me instead
describe
>> the corner I found myself in.
>>
>> Just about the time I wrote this:
>>
>> "The */coupled consumer and producer of a component/* is
defined as a
>> consumer and producer from a component, where the componentType
of the
>> component in question defines a consumer that has been @coupledTo
a
>> producer from the same component."
>>
>> ... I realized I was in trouble.
>>
>> To make this notion work, when talking about composites, we have
to make
>> normative statements to the effect of "whenever you promote
a consumer
>> coupled to a producer, or vice-versa, the "coupled"
consumer or producer
>> MUST also be promoted, and the resulting consumer and producer
MUST be
>> reflected into the componentType of the composite as being coupled."
To
>> that end, I wanted to define a notion of "coupled consumer
and producer
>> of a component." That way, I could say more simply:
>>
>> "Either both parts of a coupled consumer and producer of
a component
>> MUST be promoted and remain coupled, or neither is."
>>
>> We've also discussed that a "coupled consumer and producer
of a
>> component" must also both be connected to a channel, if either
of 
>> them are.
>>
>> I can only begin to imagine the verbal knots we're going to get
into
>> when we start applying policies, and have to introduce gems like
"the
>> coupled consumer and producer of a component" must share
the same policy
>> intents and policy sets.
>>
>> The difficulty here stems from a simple problem - producers and
>> consumers, so far at least, have independent existence, and now
we want
>> to add text that couples them together tightly while still giving
them
>> an independent identity.
>>
>> Having tried to write it up that way, I conclude it is far more
natural
>> to reflect the notion of "prosumer"
>> (http://en.wiktionary.org/wiki/prosumer)
(or conducer
>> http://en.wiktionary.org/wiki/conduce?)
as Anish has stated, because:
>>
>>     * That creates a thing with a single identity, to
which specific
>>       rules can be applied
>>     * You don't have to create normative rules about
how coupled
>>       consumers and producers must be both promoted
or neither is
>>       promoted, and likewise about how they're
both wired to a channel
>>       or not. With a single prosumer, there's no
question of a split, so
>>       fewer normative constraints are required.
>>     * The policy questions, as applied to a prosumer,
are likely
>>       different than those applied to consumers
and producers 
>> independently
>>
>> The beauty of the "coupledTo" approach is that it leaves
the
>> componentType almost untouched - with just a single additional
attribute
>> on either the consumer or producer. Unfortunately, I think adds
huge
>> conceptual cost, and based on what I've seen from what I've tried
to
>> write up, it obscures the underlying intended model.
>>
>> Having come to this conclusion, and considering that I want something
>> ready for our next call, I'm going to take a run at writing up
the
>> "prosumer" approach starting Thursday or Friday of this
week. That is,
>> unless I hear from others enough that convinces me I'm jumping
the gun.
>>
>> -Eric.
>>
>
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