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


Danny and Eric's arguments have convinced me that auto-creation of 
global channels make sense. It would certainly simplify config/deploy -- 
I won't have to create a separate composite that contains only the 
channel name and then deploy it to the domain. Currently we do allow 
this for the default channel ("//"). As Eric points out, my issue wrt 
error detection can be dealt with by tools (I can have a global option 
or flag for the deployer). Given that we already allow this for the 
default channel, and channels currently require no additional 
configuration (one can have configuration, but is not required to), 
autocreation would provide a consistent model and would make simple 
deployment scenarios easier.

-Anish
--

On 2/7/2011 9:50 AM, Eric Johnson wrote:
>   To be more explicit, and echo Danny's point, I think we have four options:
>
> 1) Mandate that auto-creation of channels works
> 2) Mandate that auto-creation of channels never works
> 3) Identify specific situations where #1 or #2 are possible
> 4) Take no position (this may still imply changes to the spec, insofar
> as we highlight the point, while taking no sides)
>
> I raised the issue because #4, it seems to me, leaves the door open for
> interoperability failures. ("I deployed X over here with no problems,
> but it doesn't work over there.")
>
> Insofar as I've recall the discussion of the concrete use cases for
> global domain channels (Oracle's F2F presentation), we explicitly noted:
> no filters, no policies, and no bindings on said channels. Meaning,
> configuration optional, and it's just a name. If it is just a name, why
> can't I auto-create?
>
> Anish notes that some people like the safety net of predefined names,
> and I agree that's useful. However, that can be addressed in a variety
> of ways that aren't nearly so heavy-handed as to simply deny the
> deployment. ("The domain contribution includes references to global
> domain channel "foo" that doesn't yet exist. Continue/Cancel?).
>
> -Eric.
>
> On 2/7/11 9:30 AM, Danny van der Rijn wrote:
>> Yet all their configuration is optional?
>>
>> On 2/7/2011 3:39 AM, Mike Edwards wrote:
>>>
>>> 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?
>>>
>>>
>>> ------------------------------------------------------------------------
>>>
>>>
>>>
>>>
>>> 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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