Re: [sca-assembly] [Issue 253]: (1.2) Must a global domain channel bedeployed before it can be used?

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

Eric,

My view is that global channels - indeed
any channels - are more than a name - they have configuration associated
with them.  A system which does
not require them to be declared makes it difficult to provide required
configuration.

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:	04/02/2011 17:14
Subject:	Re: [sca-assembly] [Issue 253]: (1.2) Must a global domain channel be deployed before it can be used?

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On 2/4/11 1:37 AM, Anish Karmarkar wrote:
> I don't see this being different than say requiring that a variable
be 
> declared before it is used.
<eej>
Which might be a perfect analogy.

If the only point of a global channel is to establish a name, then 
there's actually minimal value to declaring it before it is used. Many
dynamic languages work this way - Python & Ruby. In the case of global
domain channels, for many use cases, filters and bindings don't make 
sense, so the channel just becomes a name. At which point, declaration
before use looks like ceremony over substance.

</eej>
>
> -Anish
> -- 
>
> On 2/1/2011 10:11 AM, Danny van der Rijn wrote:
>> An interesting argument for tight coupling...
>>
>> On 2/1/2011 6:19 AM, Anish Karmarkar wrote:
>>> I think this is a fine issue to raise, but I don't quite support
the
>>> auto-creation proposal. The only global channel that is
>>> 'auto-deployed' or always exists is the default channel.
>>>
>>> I would want the runtime to tell me if I referenced a channel
that has
>>> not been deployed (unless it is the default channel, which
is the
>>> exception). If I want a producer and consumer (especially
if they are
>>> in different composites) to communicate over a common channel,
I would
>>> want the system to catch typos. For example, if the producer
is
>>> connected to the channel "//omg" and the consumer
is connected to
>>> "//zomg", they would be deployed fine but my application
would not
>>> work correctly.
>>>
>>> -Anish
>>> -- 
>>>
>>> On 1/31/2011 10:19 AM, Eric Johnson wrote:
>>>>    Hi Peter,
>>>>
>>>> On 1/31/11 10:02 AM, Peter Niblett wrote:
>>>>> Eric
>>>>>
>>>>> You said..
>>>>>
>>>>> Neither of the above indicate whether or not the global
domain 
>>>>> channel
>>>>> can be used before it is referenced.
>>>>
>>>> Ah yes, the joys of a muddled brain on Monday morning.
You're 
>>>> correct -
>>>> the question is whether or not the global domain channel
can be used
>>>> before it is *created* via a contribution.
>>>>
>>>> Thanks for catching my circularity.
>>>>
>>>> -Eric.
>>>>>
>>>>> I'm not sure how you can "use" a channel
without referencing it (I
>>>>> assume "reference" means "wire to/from"),
but I think the question 
>>>>> you
>>>>> are asking is the one in the title - "can you
reference a channel 
>>>>> that
>>>>> hasn't been defined to the SCA assembly?". I
think this is one place
>>>>> where the current spec is clear.. you can't reference
a domain 
>>>>> channel
>>>>> that hasn't been defined.
>>>>>
>>>>> So it looks as though your issue is to say that we
should change the
>>>>> spec to say that it permits (in fact requires) autocreation
of domain
>>>>> channels. Presumably these channels would have to
be created with
>>>>> default attributes (though I know you think they shouldn't
have
>>>>> attributes at all).
>>>>>
>>>>> 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: OASIS SCA Assembly<sca-assembly@lists.oasis-open.org>
>>>>> Date: 31/01/2011 17:19
>>>>> Subject: [sca-assembly] NEW ISSUE: (1.2) Must a global
domain channel
>>>>> be deployed before it can be used?
>>>>> ------------------------------------------------------------------------
>>>>>
>>>>>
>>>>>
>>>>>
>>>>>
>>>>> Title: Must a global domain channel be deployed before
it can be 
>>>>> used?
>>>>>
>>>>> Target: Assembly 1.2 WD 03
>>>>>
>>>>> Description:
>>>>>
>>>>> Via the "@target" and "@source"
attributes defined on a consumer&
>>>>> producer, the assembler can reference global domain
channels.
>>>>>
>>>>> In section 5.8, the presumed to be normative text
reads "SCA runtimes
>>>>> MUST support the use of domain channels [ASM????]."
That is followed
>>>>> by:
>>>>>
>>>>> "To create a Domain Channel, deploy a composite
containing a channel
>>>>> directly to the SCA Domain (i.e., do not use that
composite as the
>>>>> implementation of some component in the Domain)."
>>>>>
>>>>> Neither of the above indicate whether or not the global
domain 
>>>>> channel
>>>>> can be used before it is referenced.
>>>>>
>>>>> Proposal:
>>>>>
>>>>> General theme: do not require the global domain channel
to exist 
>>>>> before
>>>>> it can be used.
>>>>>
>>>>> Specific text (needs refinement?):
>>>>>
>>>>> In section 5.8, Paragraph #2, append:
>>>>>
>>>>> When contributing artifacts to a domain that contain
references to
>>>>> global domain channels that have not been created,
the SCA runtime 
>>>>> MUST
>>>>> automatically create said global domain channels,
and cannot reject
>>>>> such
>>>>> contributions [ASM????].
>>>>>
>>>>>
>>>>>
>>>>> ---------------------------------------------------------------------
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>>>>>
>>>>>
>>>>>
>>>>>
>>>>>
>>>>>
>>>>> ------------------------------------------------------------------------
>>>>>
>>>>>
>>>>>
>>>>> /
>>>>> /
>>>>>
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