There are problem, such as Dave Ellis will tell you related to emergency response, where the choreography pattern is vital because you do not know in advance the location and extent of the emergency and thus do not know the resources you will need to orchestrate.
I also don't see the need to change the service with a change in the choreography. I expect the choreographies are externally maintained patterns.
On Apr 12, 2009, at 7:11 PM, Mike Poulin wrote:
I am in favour of Orchestration for SOA 10 times more than for Choreography because the latter requires services modification for each new choreography it participates in and this decreases SOA flexibility in adopting business changes. Everything Rex said about events and policies is applicable to Orchestration as well but Orchestration is much cleaner from SO perspectives and much more dynamic. In Yahoo! SOA User group, we have discussed this topic a few times and always concluded the advantage of Orchestration over Choreography for service-oriented environment.
----- Original Message -----
From: "Rex Brooks"
To: "James Odell" , email@example.com
Subject: Re: [soa-rm-ra] SOA-RA(F) reorganization
Date: Sat, 11 Apr 2009 16:47:14 -0700
If we had spent more time on Choreography, where events trigger
policy-based rules for transactions and/or communications, it would
be somewhat easier to pull together a stand alone Policy
subsection. Of course, Orchestration also employs policy-based
rules, but resorting to a Conroller Application removes the
requirement for either human intervention based on judgment
required by rules and assessing state, or some heuristic algorithm.
I'd still just add the standalone policy subsection rather than
eliminating the Policies and Contracts which I think we need for
more reasons than just continuity from the RM.
At 7:03 PM -0400 4/11/09, James Odell wrote:
> Hi Frank,
> Hmmm. While the two "the enforcement of the two is fairly
> closely aligned" -- contracts are not necessary for Policies,
> only the other way around. Policies, IMO should stand alone on
> their own. The CEP folks argue that policies and events are
> "fairly closely aligned". I can name a half dozen other areas
> that could say the same. The bottom line is that: Policy is a
> concept that may be necessary, but not sufficient for other
> areas. Therefore, I strongly support its own sub-section.
> On 4/11/09 6:11 PM, "Francis McCabe" indited:
> Hi Jim
> Thank you for taking a look.
> As far as policies go, we have havered a little (to use a
> Scottish-ism) on how to organize it. In the RM work we closely
> identified the two -- with the distinction being that contracts
> are agreed to and policies are asserted. Once you have either
> one, the enforcement of the two is fairly closely aligned.
> On Apr 11, 2009, at 2:46 PM, James Odell wrote:
> Hi all,
> After yet another reading of the SOA-RA (Foundation?) and having
> sat through the recent spate of meetings, I have the following
> say about the reorganization of the SOA-RA:
> Overall, I think that the chapters and topics are sequenced in a
> coherent and logical manner. Perhaps, it is because I read it
> too many times now. But, I don't think so.
> Also, I understand the need to minimize the amount of work
> needed on the SOA-RA at this point in its development. We need
> to get it released for public comment - without compromising
> quality and understandability, of course.
> Having said this, the only thing that bothers me enough to
> suggest a reorganizational change is the area of Policies:
> 1) Policies, in general, are depicted in document far earlier
> than they are finally addressed (by 40-50 pages). Since policies
> - IMO - are an important ingredient in the SOA-RA, I would like
> to see them addressed earlier. (My personal opinion is that
> policies are not mentioned anywhere near the amount that they
> should. For example, they are used in events, composition of
> services, roles, and organizations. However, since this would
> involve additions to the current document, I will not push this)
> 2) I strongly dislike grouping the entire topic with contracts.
> While policies are used for contracts, Policy is a standalone
> concept - which neither depends on nor is used solely with
> Contract. (Even the OMG and W3C treat policies as a separate
> notion.) Why is this reasonable? Because policies are used in a
> variety of situations - only one of which is contracts. By
> placing Policies in lock step with (and almost subordinate to)
> with Contracts is not appropriate, IMO. 3) My suggestion:
> separate Policies and Contracts into two distinct subsections
> (e.g., 4.4 and 4.5). In short, this would provide clarity for
> the notion of Policy and not require much change to the current
> All the best,
-- Rex Brooks
Starbourne Communications Design
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