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Subject: Re: [sca-policy] Issue 54 - wire validity - proposal


Thanks for getting this resolution together.

Tackling your comments:

Assembly 57 (and the prior decision of the Bindings TC) imply that specific (non SCA) bindings can only be used in the
case where "SCA mechanisms are not being used" - and that a resolved target must be supplied.

I'll be frank and say that I was not keen on those decisions - they have real consequences.  So let's peer into a couple of
usecases and observe their effects:

A) I make a policy decision that I want all "internal" communications to be made via JMS (using a company messaging
system).  External stuff will use specific other mechanisms.  How can I do this?

In the past, we could have envisaged simply attaching "binding.jms" to those "internal" wires.  This would have had to be
done by hand - long & laborious.  A non-standard way of avoiding this would be for the runtime to provide the capability
for us to indicate that "binding.sca" == "binding.jms" for this Domain.

External attachment (once we've resolved it !!!) would allow us to define a rule that picks out "internal communications"
and then apply "binding.jms" to such references/services.  EXCEPT now, we would also have to write in the target
explicitly.  This would be virtually impossible to do using a rule.  So the idea of applying a binding using external
attachment is effectively killed, at least for internal comms (unless it's done the laborious way - one attachment for
each service and reference, one at a time).

This leaves the only "standard" way of getting what is needed here along these lines:

a) Use "external attachment", with suitable rules to pick out the "internal communication" targets
b) Apply one or more intents to those locations - intent(s) that pick out the need for "binding.jms"
c) But the binding actually present at those locations MUST BE binding.sca (to be able to use @target)
d) So we have to define binding.sca as being capable of handling whatever set of intents are necessary to
pick out the use of a given concrete binding !!!!

I'm going to dump this one into the lap of the Bindings group to show the effect of these decisions....

B) Any similar decision to A) to apply particular bindings ANYWHERE below the Domain is made equally
painful, with the same consequences.

EITHER I have to specifically identify each wire that I care about and provide configuration for it, one at a
OR I have to use a general rule, but only apply an intent and rely on binding.sca to sort it out.

C) To apply bindings at the domain level, I can at least do it as a deployment decision - ie apply the
bindings I want as I deploy components into the Domain.  But in each case, whereever I want a specific
binding to apply, I have to supply unique configuration relevant to that binding.  The idea of saying something
as simple as "connect to that component service over there" using "binding X" is gone.  You have to go
fetch the endpoint and any and all parameters relevant to that binding type and endpoint.

So much for SCA simplifying things.

I now discover an empty bath - no water, no baby.
I am rapidly turning into a revolting peasant ;-)

Yours,  Mike.

Strategist - Emerging Technologies, SCA & SDO.
Co Chair OASIS SCA Assembly TC.
IBM Hursley Park, Mail Point 146, Winchester, SO21 2JN, Great Britain.
Phone & FAX: +44-1962-818014    Mobile: +44-7802-467431  
Email:  mike_edwards@uk.ibm.com

David Booz <booz@us.ibm.com>

17/06/2008 19:03

[sca-policy] Issue 54 - wire validity - proposal

This completes my AI 2008-06-16-03.

Please take careful note of the proposed changes and the two comments as I
discovered an interesting twist in the resolution of Assembly-57 which
spawned this issue in the first place.

(See attached file: Issue54_proposal_on_wd-05.doc)

Dave Booz
STSM, SCA and WebSphere Architecture
Co-Chair OASIS SCA-Policy TC
"Distributed objects first, then world hunger"
Poughkeepsie, NY (845)-435-6093  or  8-295-6093
http://washome.austin.ibm.com/xwiki/bin/view/SCA2Team/WebHome[attachment "Issue54_proposal_on_wd-05.doc" deleted by Mike Edwards/UK/IBM] ---------------------------------------------------------------------
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