Fw: [sca-assembly-comment] NEW ISSUE: (1.2) Promotion of consumers andproducers undermines composability

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

Folks,

Forwarding to the main sca-assembly
TC list....

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
----- Forwarded by Mike
Edwards/UK/IBM on 09/04/2010 09:18 -----

From:	Eric Johnson <eric@tibco.com>
To:	sca-assembly-comment@lists.oasis-open.org
Date:	08/04/2010 18:18
Subject:	[sca-assembly-comment] NEW ISSUE: (1.2) Promotion of consumers and producers undermines composability

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Target: sca-assembly-1.2-spec-wd01.doc

Title: Promotion of SCA consumers and producers undermines composibility

Description:

In the assembly 1.2 WD 01, consumers and producers are identified as part
of the "component type" of a component, whereas "channels"
are limited in scope to the boundaries of a composite.  This is contrary
to the rest of SCA, where the indication of the communication between components
surfaces in the component type, currently as a service or reference. 
When needed, services or references can establish concrete bindings, but
otherwise communication needs are exposed at the boundary of a composite. 
In the case of producers, consumers, and channels, not only can bindings
be applied, but also "targets", which then either hide endpoints
within a composite, or expose them globally as part of the "global
domain."

This makes composition of applications using eventing more difficult.

Further, although producers and consumers can refer to the same target,
this is an awkward way for these two constructs to establish that they
intend to operate on the same "destination".  When building
a composite the composite developer may wish for one component to produce
for a channel, and a different component to publish on the same channel,
and then promote the combination of producer and consumer.  If the
developer only promotes the consumer, or only promotes the publisher, that
would be misleading to the composites using that component.  Perhaps
it is even an error.

Here, then, are two problems:

• "target" channel references are a weak way to couple the use of the same destination.
• target channel references can be to a domain channel, thus undermining composability - either by collisions in the naming of target channels, or by forcing special knowledge of which channels are used where.

Proposal:

Instead of promoting consumers and producers, promote channels.  Move
the filter and eventType information on consumers and producers into the
channel.

-Eric

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