| Michael,
I see the disconnect. My view of choreography is I receive a recognized message and follow through with appropriate activities. My role in a response is coordinated beforehand, but this is typical for defining and practicing emergency response. Part of the incoming message tells me others who are part of the response, and that tells me something about who may be next in a chain to receive information. Alternately, my response could be public and sufficient for others to move forward simply due to the change in shared state.
Again, I have not looked at WS-CDL in a long time, but I agree a choreography would be limited if it could only carry out one static script.
Ken On Apr 13, 2009, at 12:02 PM, Mike Poulin wrote: Exactly, Ken, "if...different sequences of actions are required, these can be modified without modifying the services themselves". This is possible ONLY if services do not know who, where, why and when use them. That is, they DO NOT operate under current Choreography standard which requires all this knowledge to be in the service itself. If paramedics, Walmarts and alike operate with available services being service orchestration services/engines/components by themselves, they will know up-front (before engaging a helper service) what messages to expect and in which order because the engagement is made based on Service Description and implicit/explicit service contract that define interaction interfaces. - Michael ----- Original Message -----
From: "Ken Laskey"
To: "Ellinger, Robert S (IS)"
Cc: "Mike Poulin" , "Rex Brooks" , "James Odell" , "soa-rm-ra@lists.oasis-open.org"
Subject: Re: [soa-rm-ra] SOA-RA(F) reorganization
Date: Sun, 12 Apr 2009 22:00:47 -0400
Think of the scenario this way:
FEMA comes up with a generic coordination of assets for an emergency. So the police are prepared to receive certain messages and perform certain actions (including the use of and reporting through SOA services). The paramedics are prepared to receive other messages and respond. The Walmarts are prepared to receive messages that certain supplies (such as bottled water) are needed from certain stores. The public transportation is prepared to receive messages that would indicate putting predetermined evacuation patterns in effect, and their responses trigger other messages.
Note, we have lots of folks who are prepared to receive messages, possibly initiating service interactions, and respond as agreed.
If a review of the predetermined coordination decides different sequences of actions are required, these can be modified without modifying the services themselves.
Ken
On Apr 12, 2009, at 9:49 PM, Ellinger, Robert S (IS) wrote: I suspect that if there was more than one, say two or three, services offered that performed the same function, that a service could ameliorate the condition of SLA build-up, which is similar to tolerance build up, by dynamically choosing various fallback services and could, with a concierge service, discover a reasonable set of services to perform the function of some service that is unavailable to due a backhoe outage or an operator fatfinger or... Choreography would then be "in play" even though the service might be orchestrated under normal conditions. Bob Michael,
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.
Ken 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.- Michael ----- Original Message -----
From: "Rex Brooks"
To: "James Odell" , soa-rm-ra@lists.oasis-open.org
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.
Cheers,
Rex
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.
>
> -Jim
>
>
>
> 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.
> Frank
> 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
> document.
>
>
> All the best,
>
> Jim
>
-- Rex Brooks
President, CEO
Starbourne Communications Design
GeoAddress: 1361-A Addison
Berkeley, CA 94702
Tel: 510-898-0670
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